I am new to triathlons. I have done 2 sprint and 2 Olympic distance races and I will be doing my first 70.3 in June. I have become addicted and upgraded from a road bike to a P2. Are aero wheels (likely used) worth the price? I averaged about 21 mph in all my races on a road bike and seem to be going a tad faster on P2; will I see a difference in aero wheels compared to my stock wheelset? Any advice will help!
The difference between stock wheels and aero wheels is quite significant, sometimes as much as the difference between a road bike and a tri bike. So to put it simply, yes you will see a difference.
Whether they are worth it or not is really only a question you can answer, but if you really are hooked on triathlon then I would venture to guess it wouldn’t be a purchase you’d regret.
Yes, they are worth it. Sometimes you can see a bigger speed bump going from box rims to aero wheels than from changing your frame set. The best bang for the buck is probably a Flo 30 front and a disc cover for your existing rear. Otherwise maybe look into a Flo 60 front and disc rear or a HED Jet 6 front/disc rear. Personally, I’m a fan of aluminum braking surfaces. When in doubt about rim depth for the front (30/60/90) error on the shallow side.
Congrats on your new addiction 
I would check other boxes first if you haven’t like:
skinsuit, aero helmet, fast tires and latex tubes.
aero wheels make a significant difference but are fairly expensive so get them once you get the low hanging fruit.