I'm a 49 year-old that rides in the 20-23mph range for 90minutes(last outing). I've got some Ritchey Aero Pro's and am looking for suggestions on an wheelset for the Florida Ironman in November. I can't afford the pricey ZIPPs and am worried about the cross-winds in Florida. What would you suggest and can I get a 1/2 mph increase by adding a mid-range upgraded wheel set?

I don't think you will get 1/2 mph out of an upgrade. I'm no wheel expert; but, when I was just looking at wheels the top of the line may have gotten me a few minutes at IM distance. At the speed your are at, body drag is more significant. Have you had your fit checked for the best aero position? Also, you may want to get fresh bearings, hubs and greese to tune up your current wheels.

Look into renting a set of wheels from Inside-Out Sports. They are the bike support for all the IM races and a lot of people go this route. Plus, no big investment into a wheel you may or may not be satisfied with.