Next upgrade - wheels or bikes?

Hi,

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.

Thanks,

Yossi