DC
YO! You know the only dumb question is the one you.... Yeah, it's probly not a good time to upgrade. I read the posts re: Your TopFin15. I agree with what was said there. Your filter will be fine for that 10g. If you just have to upgrade, do what CFMike says - keep the old one when you add the new one. But, think about it- for the MSRP of a good filter you could get another starter tank from the LFS. Then you're back where you started with a filter you don't really want.
Chances are you are going to want a bigger tank real soon. Save the money and put it towards that 55g.
Goodluck!