I like valve covers and stem washers!
 

Valve stem covers: keep the dust off, protect teh presta valve from damage, keep the stabby end of the presta valve from stabbing your hand while working on the bike

stem washers: keep the stem from sinking into the tire when I push the tire pump valve onto it

I can't see why people don't like them!!

Valve covers and the stem nut are like ice cream. Some people like vanilla, others chocolate, neither are wrong.

For the record, All my bikes are PV except for two I keep in Mexico. On the SV bikes I use valve caps to keep salt water out of the valve, and their molded valves don't use stem nuts. On all the other bikes (PV) I never bother with caps, and as for stem nuts, never with tubulars, and generally not with wired-ons, but on my 26" commuter with fairly fat tires I leave them on loosely to make pushing the pump on easier.

I buy tubes with smooth valve stems - easy on & off with the pump head, and no threads for a stem nut.

Some tubes have a threaded base for the nut and the rest of the stem is smooth. That's what I use. Unfortunately, the threads don't come out of the rims I have far enough to thread a nut on it, so it's entirely useless to me. I don't use the caps, either.

Keeps the dust off? How is this a real advantage?

I know, right?

I like valve stem covers, as a little touch of frilly "bling." Mine are red and look way cool on my wheels. Not practical, I know. But there it is.
Stem washers? Always. Too practical, IMHO, to be chucked in the trash.

Keeps the dust from getting in the tires.

I assume you mean the tube. In that case, think about this...if there's any pressure at all in the tube when you open the nut, nothing is getting in. Even if a little dust did get in there, so what?

Extra weight.

Uh huh, and how much dust do you think it would take to negate the weight of the cover that's used to prevent this?

If it wasn't for the comment about the stem washer (the only substantial benefit pointed out in the original post), I would have thought this was a joke thread. Post #9 solidified it though.

All that dust getting in the tube can add up in weight. And how are you going to get it out? Plus dust can clog the valve itself, and abrade the tube from the inside. Finally, the tube manufacturers are experts (what's your expertise?), and they obviously think tube valve covers are a great idea and include them. Pwn.

Enough dust & dirt inside the tire (between tube and inner tire carcass) can also act like very fine sandpaper, slowly abrading away at your inner tube. POP! Happened on a used MTB I picked up. Both tires had about a tablespoon full of very fine dirt in them. Tube split about eight inches lengthwise.

Plus all that caked on dust and dirt on the valve is gonna act like sandpaper on your pump valve every time you inflate your tires.

You are push-ing the pump head on too far, There is a smooth section on all
P/V stems, right below the thread for the cap.

I stopped wearing out Presta air pump gaskets when I quit shoving them on too far.

Silca track pump..

I knew there was a reason for threaded heads and stem washers. I feel so much better about using them now. :)

The stem covers are put on by manufacturers to prevent the pointy bit of the stem from puncturing the tube while it's all wrapped up nicely for transit. Nobody likes buying an already been popped inner tube.

My bike doesn't have a single item on it that isn't totally necessary to its operation... except maybe the bar tape, rear brake and front derailleur and shifter.

These useless bits of junk you speak of serve no purpose for me. Valve caps? Thoroughly pointless. Valve nuts? Easily replaced with technique, thus also, pointless.

Do you think valve caps are totally useless on your car, truck or off roader? Just try to top off a tire with the valve packed full of mud and crud. Then hope the valve seats properly to prevent a slow leak after you are done.

Valve caps?!!!!

First it's chain lube, then wheels, spacers on top of stems, carbon fiber, etc. Now we're down to debating valve caps. Come on, they're free with tubes, use them if you want, or chuck them if you don't.

Is there nothing folks don't get worked up over?

Stem nuts and valve caps are not PRO...

Stem nuts are evil. I had like three tube failures at the valve where the tube peels off of the valve, I was told to not use the nuts on them any more, no more failures.

I use caps religiously. It's not that dust or grit will get into the tires but rather that a spec of grit could be blown into the seat of the valve seal and cause a leak in the stem. Around here things are wet enough that after a few rain rides the valve caps are covered in stuck on dirt and sand. Adequite evidence for me that using the caps is a wise move.

I'm familiar with the Willamette valley thanks to my model flying. I've attended many contests in the seed grass growing areas there over the years. I'd suggest that your area of Corvalis sees enough rain that if you're riding in it or if you do off road riding that I'd be worried about picking up grit that would get into the valves as well.

What about graphics and decals? Do you have dust hoods over your brakes/shifters?

No.