I've been doing triathlons for the past two years, mainly short distance. I train both on flat roads, adding the occasional climb.
I currently own entry level bikes (Merida 905) - basic aluminium frame, stock wheels and (not so entry level) ultegra components. I also use PD aerobars.
I have about 1KUS$ to spend on upgrades going into next season, and I see two options:
1. Buy new bikes - sell my bikes, add the 1K and buy new, or used, bikes.
2. Upgrade the wheels on my current bikes.
The purpose of the upgrade is simple - improve my time on the bike leg.
Right now I like option 2 better. Since I have a good set of components and I already own aerobars, I believe that upgrading my wheels will provide me with a lot of added value. If I decide to upgrade my bikes, I might be able to find bikes with a better frame (perhaps even used carbon frame), but I doubt if I can get bikes with better components, and my feeling is that a better frame will not help me cut my bike leg time as a good set of (again, probably used) wheels might.
Any thoughts or suggestion would be highly appreciated.
If your bike fits you well, than a new frame won't make you that much faster (or possible not even faster at all...).
I spend the money on wheels, but only if you have already had a bike fit, if not, that's where I would spend some of the money. You constitute the vast majority of the drag, so improving you position will yield the most noticeable result. Add comfort and efficiency to the mix and it's pretty clear why this is.
Definitely wheels... a few years ago, I had to replace the wheels on my bike (because of a cracked rim). That year my speed increased by over 2 km/h on average. I hadn't done anything different training wise.
If you are currently riding the stock wheels on your bike, then just upgrading to a nice racing wheel will give you free speed. This isn't even going to carbon fibre race wheels... just a high end wheel will have better quality bearings, which is a big part of the equation.
As was mentioned before... spend some money on getting a proper fit and the remainder on a good set of wheels.