I have heard the advice not to try to put on a top after the swim (experienced first hand), but is it worth it to buy a Tri specific top for a sprint tri? The swim portion will be in a pool, so wetsuit is not an option. I have high hopes of a top 5 finish, so time is important. I am also concerned with how much a top may slow me down in the water.

Any advice is appreciated.

I suppose the answer depends on what you want to spend, and what the alternative is. I can think of five possibilities so i will list them, and if you have another idea then tell the internet what you were planning to do so we can yell at you. (joking, or for some people maybe not, but I am not planning on it)

1. Wear a baggy T-shirt during the swim.
2. Put on some kind of something in T1
3. Wear a cycling jersey during the swim
4. Just go shirtless the whole time, or sports bra if you are a girl, and assuming the tri allows it.
5. Buy a tri top and wear it the whole time.

Options 1 and 2 are frankly terrible ideas so don't try either.
Option 3 would be fine, may slow you down a bit.
Option 4 depends on how many little kids you make cry at the beach, or referees depending on the race.
Option 5 is probably the way to go, but involves a bit of money, and may make you go a bit faster.

And as for your concern about how much a top will slow you down, do you mean a tri top or a regular top?
Tri tops are designed for swimming, They should not slow you down at all, and higher end ones should make you faster, but just by a bit.

The time differences in the short tri distances (like sprints) are much shorter than the longer races. Thus, if you really want to be competitive and shoot for a podium/1st place finish I'd recommend getting a tri top or (assuming the rules allow it) go shirtless.

A bicycle jersey would work in a pinch like sirious above mentions but unless you have one that is race cut and actually fits you like it was intended you'll probably be pretty annoyed with how baggy it feels during the swim.

My concern with the Tri top is the small pouches on the back designed for holding nutirition (not needed in a sprint). Some have overlapping seams, but some (cheaper) have open pockets which would seem to act like a drag in the water. I have already purchased a nice top with the overlapping seams, but not sure I really need it. I admit, I am a cheapskate.

ummm, $100 2XU tri tops have open pockets, and i think it's fine for three reasons: 1 they have mesh so water would go through the pockets if it got in (a little drag yes, but not more than a few seconds worth), 2 they are tight so not much water would get in anyway, and 3 they are on the back, so not to much water is flowing there anyway.

Ok. Bought a top (actually exchanged). I didn't want to try to put a top on after the swim. Hopefully it works out well.

I did a race this spring that required a top on the bike and run, so I bought a Zoot tri-top. I liked it so much I have worn it in every race since. It's nice to have the little pockets to put a gel in if you want. The top is supposed to fit skin tight, like the shorts. No way is water going to get in the pockets and slow you down.

Must have been the top! Had a good race today with my best swim time (12:50 for an 825y swim).

I'm not real experienced but, for my first tri, actually an aquabike sprint, I purchased a Zoot top and then biked in my jammers. It worked well and I had a place to put a couple of Cliff blocks.