After ~1000 km, I got a non-repairable cut in my last GP4000, so I had to replace it with a new GP5000. Since then I've only ridden it on the trainer while Zwifting, so I don't know how they feel differently. I may be "wasting" wear on nicer tires, but I like having them available if I go out on the roads.

the watt saving of the GP5000 is meaningless in every way for 99.99% of the riders out there.

Why?
For a typical person, 5'9", 175 lbs, going at 20 mph without much wind, you're probably pushing a mininum of 230W. A few watts saving means NOTHING.
If there's a slight headwind, you're probably doing 270-300w.

But if you can expend only 200 watts for the same speed, you can go further for the same tiredness at the end of the day.

Or for the same 230 watts you can go faster.

It's watt savings per tire. And it can be significant compared to what you are comparing it against. (20-30 watts when compared to Gator Hardshells, for 10-15% savings, for example.)

Your example of wind is a variable. Rolling resistance is a constant.

Even at 5-10 watts total savings, the GP5K'stires themselves are ~$15‐30 cheaper per tire than the next comparable competitors. I'd hardly call that wasted effort.

I'm coming around to that frame of mind myself, especially since we're not racing anymore.

I see you points. But your scenario only mainly comes into significance if 1) you're riding steady-state, 2) on the flat, 3) without much wind, 4) without much cornering, 5) your front and rear weight distribution is 50/50 ratio.
In real world situation, things are not this ideal to allow you to realize the rolling-resistance superiority of the GP5000.
The advantage of drafting makes the advantage of rolling resistance a low priority on the list of "things to do". I see plenty of (presumably timid) riders not willing, or unable to draft effectively.
In mountain descents, cornering counts, and the GP5000 is not the top performer in cornering, not close.

while the argument of "if you could use less wattage to go the same speed, then you'd be able to go further" sounds compelling from a strictly quantitative point of view, but in the real world riding, real world century'ing with your buddies, real world racing, nobody has won or lost anything based on tire rolling resistance. It makes very little sense to place great emphasis on tire rolling resistance between all the "top tier tires". And this is my main point. (And Gatorskin is not a top tier tire.)

Rolling resistance doesn't go away in those situations. Better rolling tires are still better rolling in various situations; drafting, sprintng, up a climb, down, headwind, tailwind, etc.

I'd rather spend some money on some nice, comfy tires than spend 5-10x that on some ceramic bearings for my derailler pulleys that might give me a fraction of those watt savings and ride some hard, crappy tires.

I really liked the performance and cornering but after three days and three flats I took the GP5000 clinchers off. Not sure if there'd be much of a demand for some used GP5000s (400 miles) on eBay.

After my mellow is less harshed I may try the tubeless.

Umm, what exactly do you think these "top tier" tires have in common?? It's low rolling resistance. That is precisely what makes a tire fast. When you can combine that with decent puncture resistance, and good grip, you have a fantastic all around tire that you can even race on, like the GP5K.

Someone who can go fast on a crappy tire, can go even faster on a good tire, it's pretty simple. Mechanically, tires/tubes are one of the best bang for your buck improvements you can make. Position/kit being the biggest areas for speed gains.

No it doesn't. By reducing aerodynamic drag and allowing higher speeds, drafting makes rolling resistance more relatively significant: it becomes a greater fraction of overall resistance.

Can someone show me just ONE example where rolling resistance of say a GP4000/5000 tire vs say a Schalbe, Vittoria, Michelin tire make a difference in anything?
Meanwhile, I shall continue to wait for any bro and Fred in their Conti GP tires to pull away from me and my cheapo Vittoria Rubino's. Yawn.

This question being asked - and mostly the matter being discussed - is less about how different brands compare with each other than how different types of quality tiers of tire compare. Nobody in here is saying that you're an idiot if you run Vittoria-branded tires. When people are saying "GP5000 is a noticeable improvement", they're saying it's a noticeable improvement over Conti's entry-level tires (since that's what the OP asked about), not that it makes Corsa Speeds look like garden hoses or whatever.

I run Michelin Power Protection+ for my morning training rides so I can spend more power for the safe speed on the MUP and get in a better workout while time-limited. Different perspective on the situation.

But never a Gatorskin.

As HTupolev mentioned, it's not necessarily the brand, but the model. I'm sure all the top tier tires are pretty similar in performance. I don't think anyone can tell the difference in a few watts, but once you start talking 10/15/20w, you can tell.

I can beat a lot of people on my 40mm knobby gravel tires, it doesn't mean that I'm not faster on a faster tire.

The tires save a handful of watts - not important.
The race-fit jersey and aero road helmet saves a handful of watts - not imporant
An aero frame saves a handful of watts - not important
Aero wheels save a handful of watts - not important

Add all these things up, though...? The difference matters.

Let me put it another way - leaving aside solo training/winter wheels where speed doesnt matter, why would you give up the benefits, even if they are minimal? I mean, if there are benefits that you prefer in other tires, sure, i get it - hell, as I said earlier in the post, i dont use GP5ks for group rides, preferring the ride quality of Turbo Cottons instead, even if they cost me a few watts - but spurning free watts, no matter how few, just because you think it doesnt matter seems illogical.

That said, i hope more people racing M45-49 feel the same way

Continental Competitions are one of the top tubulars you can buy from Continental.

Pros don't use Continental Competitions, they use Competitions Ltd., which the public can't buy.

Guess what the difference is? Guess why they have that difference?

You have chosen... wisely.

Latex tubes?

Bingo.

The reduced rolling resistance..."makes a difference."

I've found them on Amazon and elsewhere for near $80 for a pair. I personally feel like at that price point they are a worthwhile investment. Been using them on multiple bikes, in multiple sizes, all without issue.

The issue with your argument is that
1) most people on the internet buying these tires are not racers. It's like that old baldy guy dirivng his 700hp Ferrari down the ocean boulevard. The Ferrari gives no advantage over a Camary when you're crusing at 45 mph down the boulevard. Same with GP5000.
2) the "watt saving" shown labs and in the wind tunnel are based on controlled environment that is not a true representatio of real world. Sure you'll still save some watts, the but watt saving in real world is not seen in a controlled environment.

Now if you tell me that guys are riding on a metal drum in a wind tunnel, in a static position, in a static power delivery like on a tire drum test rig, then sure... by all means go get some GP5000.

And what about handling? GP5000s suck compare to Vittoria and Veloflex Corsa as far as giving feedback around corners. On a mountain descent, I can pull out 3-5 meters on each corner using Vittoria and Veloflex compared using a harder tire like the GP5000. Does 3-5 meters per corner count when you're trying to go fast? Of course it does. Does this advantage show up on the tire drum in the lab? Of course it won't.

And round and round we go...

Apparently you can't handle a bike very well. I routinely distance people in corners while riding Continentals.