Rear Derailleur upgrade?

You'd get crisper shifts and save a bit of weight, but the performance improvement would be minimal since you'd still be using your relatively-sloppy Sora shifters (assuming you have Sora shifters).

Do you have aero bars? If not, that's the best bang-for-your buck upgrade you can make.

Are you unhappy with the shifting of your current RD. As Jim says, changing just the RD won't help much. The old saying is, "Don't upgrade, ride up grades."

If you don't have clipless pedals/shoes, get them first, THEN aerobars, then save your $$$ for race wheels OR an upgrade to a nicer bike.

Bear's right...I always assume people are riding clipless, but you know what they say...

Here's my setup...

• Fuji Finest 2004 (specs and stuff here - http://www.fujibikes.com/road/bike.asp?category_short_name=road&myArray=87,88,89,90,91,92,93,102,94,95,96,103,97,104,106,99,98,100,105,101,107,108,109,112,110,111,113,114&myArrayID=11&yr=2004)
• Sora everything component-wise
• Look Keo Classic Pedals
• Profile Century Aerobars

Probably going to get a new tri-bike at the end of the year, so I don't want to spend too much money on this one right now. Doesn't sound like much bang for my buck getting a new derailleur.

Does it shift? if so, leave it alone. 

 You have a perfectlly adequate set-up right now.

Upgrade-itis is a terminal and tragic affliction.

Use the money you would have spent to take your SO to dinner.

Better yet, donate it to the buy-the-bear-a-litespeed-blade fund. Once I meet my goal I will shut-up about how fast red bikes are. Donations are tax deductible only if you have a hankering for federal prison.