As long as you're not over stocked I think the filter you are currently using should be fine on the 29g. Stuffing it full of bio media will help as well (adding more in addition to what came with the filter) if it's possible.

Sometime we just have to stop, look and listen and appreciate what we already have. (not to mention that $140 would go along way towards another tank

As smiley said it's really kind of up to you if you want to go the route of another type of filter or a larger one.
Sometime I tell myself "if it ain't broke, don't fix it".

Enjoy your fish.