First, about me: I have been racing for 2 years. Have the points to cat up to 3 but want to win 2 races as a 4 before doing so.

I didn't lift weights when I first started racing because like you, I didn't think there would be any benefit. Howerver, since I started about 6 weeks ago I started winning preems in the local crit. Another benefit was with my jump. Before I started lifting I used to have trouble with people getting on my wheel when I would accelerate but now that I can put out more power in a shorter amount of time I find I can shake most people in most situations. It also helped my sprinting and 1-2 min efforts. All the talk about bulkin up and getting slow...I don't believe that. The stronger you are the faster you will go.

If you are going to be racing I'd say lift weights. If you are not going to be racing you will probably have more fun just riding.

From what I have read these are the benefits to specific lifting excersises:

Squats: increase leg power so you can push larger gears.
leg extensions: same as squats.
leg curls: not sure what the benefit is but I do them anyway...probably to avoid muscle imbalances which can lead to injury.

rowing: develops upper body for sprinting
pull-ups: again not sure what the benefit is but I do them.
push-ups: these are good to develop sholder muscles that will stabalize the shoulder if you crash in such a way that will break your collar bone. ie. decrease the probability of injury.

core: the more you do the better.

Also, lifting weights will help increase bone density which will be needed if and when you crash to avoid a break.

Have Fun!