There's your answer. Where I can I always wear one. I don't usually do sprints but in my Olys I wear them. Unless you are on the podium the confidence, additional speed and buoyancy (esp if you are an average or below avg swimmer) are sefinitely woth the extra 30seconds removing it at T1.

I wear one any time it's legal. If you own one and are comfortable in it, I would say go for it. Nobody will question your manhood for wearing it in 72 degree water.

Conventional wisdom says that wetsuits help slow swimmers the most, advanced swimmers the least, but they do help almost everybody go faster.

The only time I did not choose to wear a wetsuit was a race last summer where the water was over 78, but racers could wear one if they didn't want to be considered for overall/AG awards. Not that I am EVER a podium threat, but I chose to go without for practice purposes in case my A race that year was also too warm.

US divers?...sounds like a diving wet suit..?
There is a huge difference between a tri suit and suits for diving and what not...mostly being that tri suits have much more freedom of movement and are cut for swimming...I never have, but know of folks who raced their first races in diving suits and didn't have a good experience...
Have you explored renting?

Surfing wetsuits are still not great for tris -- the big difference will be the shoulder construction. Surfing suits are made to keep you warm, not to let your shoulders work like tri ones do. I'll second Anton's renting recommendation. Many places will also sell off rental suits at the end of the season, so you can try it and race in it this year, and if you are hooked get it at the end of the season.