Should I upgrade my filter

I have a 36 bow front aquarium that is relatively new, I set it up at the beginning of May . I'm cycled and all the fish are fine, no problems. I have a Aqueon 30 Power filter, BTW this is a FW tank. Reading through the different posts I'm wondering if I should have used a larger filter (more is better I'm learning). Again, no problems with the fish, I have 5 harlequin, 5 cherry barbs, 3 platys and 2 guppies, and a pleco. Is this filter adequate (or good) for this size of tank and number of fish? (Also, I have about 7 plants.) How would I go about upgrading if I ever wanted to (or if you recommended it)? Would I run them side by side for a month or two until the new filter is "cycled". Also, how often should I change the cartridge? I've read that I really don't need to change it as often as they suggest since it's just a money maker for the company. I do a 25-30% water change weekly and clear out the water intank on filter. Just curious on that. Hopefully that's not too many questions for one post.

Thanks!

That actually sounds like a better idea, having two filters. Thanks!

Krytan, sorry for the delay in getting back to your question.... not sure the offical name of my pleco. He's dark with spots and I know he's going to get big, 10-12". He's about 2" now. I'm hoping to convince my husband to let me get a 55 gal before the end of the year and I'll eventually transfer him to that tank. Got my second filter and it's up and going. Thanks.