Can you define "springy"?

If you want to upgrade your bike, make wholesale changes. Don't get a tire 5 grams lighter, or a 10 g lighter stem. Do big changes or don't do them at all.

If you're making upgrades, make them to pieces you can transfer to a new bike, or use for a long time. For example, I have a favorite saddle type (marketed at some point as the Titanio 2000) that I've been using for probably 10 years. I have a few of them now, and I move them from bike to bike. Another example - a favorite bar shape (there, too, I've been using the same bar shape for about 20 years). Pedals too.

Wheels fall under this category as long as your drivetrain doesn't "obsolete" them. For example, a 10s wheelset can work with future bikes. Also wheels end up "completing" another bike. You can get wheels now, get a frame/kit later, and you'll have a complete bike.

You can also get expensive, one-time parts. I'd include seat posts and stems in this category, or cranks. Things that don't wear out quickly and, hopefully, can get moved from bike to bike. I use Thomson posts, Ritchey stems, and I've been moving them around too. When I got a frame with a wider seatpost (31.6 mm instead of 27.2 which is what all my other road bikes have) I just got a Problem Solvers spacer and used the 27.2 in the 31.6.

If you upgrade something for fit (longer stem for example, or a nicer bar shape) then get rid of the old piece. If you upgrade for weight, hang onto it.

I'd do, in order of cost/effectiveness, fit pieces (bar, stem, saddle), gearing (a close ratio cassette makes a difference), tires, and wheels.

For clinchers get a kevlar bead tire, typically under 250g for a durable tire. This is an area where most manufacturers cut corners - either a super light, super fragile tire or a heavy one.

For wheels get something aero. Don't waste your money getting a functionally identical wheel (Ksyrium whatever) that weighs 200-400 grams less. Get a tall aero wheel, 50+ mm rim height (I'd try and hit 60-80 mm). Save your current front wheel for windy days, get a lighter one eventually.

The upgrades in drivetrain parts gets you less function. Yes, upgrading to higher quality (thicker/stiffer) chainrings really makes a difference, but only in how you perceive the bike. It won't buy you mph like wheels, or a better position, or increase comfort like a good saddle. I'd save that for your next "kit" or group purchase.

cdr