Buy Nashbar carbon frame and swap everything over. Get Vuelta Corsa Lites on sale for $225 or so, 1570 grams.

You won't save much weight or gain much performance upgrading the drive train unless you go Dura-Ace or SRAM red.

21.6 lbs ready to ride is a good weight, really.

Seat post can save you 100 grams? Are you using steel? I bought some Chinese carbon for $35, 180 grams.

W40s weigh about 300 grams--40 grams less than the equivalent Shimano 540s. I guess for $100 you could get Ti/magnesium ... for $120, Time Xpresso 10s at 192 grams ...

for $500 you could get a frame and fork combo at 3.5 lbs.---maybe 2 lbs. less than what you run now.