This is a good thread.

My own view is that it's not worth it to spend a lot of money for weight reductions unless you're a serious racer. Let's take a fairly dramatic example.

Suppose you normally produce about 250 watts on a 5% climb and go about 11mph, an ok pace. Suppose you added 2kg to your bike, about 4.5lbs, and made no other changes. How much time would you lose?

Well, what your lighter self would ride in an hour of relentless climbing at 5% your heavier self would do in 1hr 1 min 10 sec. So the 4.5 lbs would cost you one minute ten seconds over 11 miles of continuous 5% climbing.

How much money is it worth to you to get rid of this weight?

Keep in mind, too, that we're talking about the difference that 4lbs of additional weight makes, and not the tens of grams one usually deals with in dropping weight from a decent road bike. If you've got a decent middle range bike-- a Trek 1200 or something-- it would cost several thousand bucks to upgrade to a bike 4lbs lighter. Is that worth it?

Also remember that if you're a faster rider to begin with, the time gains from less weight are even less.

You shouldn't forget, either, that typical rides with clubs or even in local races aren't up continual climbs, so the time cost on typical club rides would be much less than that minute-ten. And of course there are all of the other factors that tend to keep clubs together on the road, even with significant variation in bikes and riders.

Now a little time means a lot in a race. But for my money, if you're not racing seriously the weight reductions aren't worth the jump from middle- to high-end bikes. Of course, there are other benefits to higher end bikes, better gruppo, better style, maybe more durability, whatever. If those things are worth it to you, that's another topic. But the weight benefits are overestimated by many riders, I think.

One other thing that's worth mentioning are the common comparisions among realizing time gains by losing weight on the bike or on the person or by gaining strength. Even some people above say it's cheaper to lose weight on your body than on your bike, for example. This is true, but it isn't the relevant comparison. Even if you decided to put a lot of effort into losing weight on your body or in getting stronger there's no reason you couldn't make your bike lighter also. So the real question is whether the money is worth the time improvement from bike weight loss, whatever else you decide to do to go faster.