I am in the same situation as you. I *almost* spent the money to put aerobars on my road bike (would require a seat post change too) but decided against it because at best, it would be a temporary fix and at worst, I'd be miserably uncomfortable. My road bike fits me perfectly, and I really don't want to mess with it.

So yes, I'm thinking I'll want a tri bike. If for no other reason than the fact that I want a perfectly dialed in fit and I have a generally hard to fit body. I just got a bonus at work (yay!) and it's going into a savings account while I shop around (and save some more).

I'm waiting until next year though. I don't think a tri bike will help me much on my last two tris of the season (both very hilly courses) and while it would probably make a huge difference in the tri I'm doing on Sunday (straight, flat course), it's too soon to bother.