I have a 36g with 2 Penguin 200 Bio-wheel Power Filters. Did adding the second Penguin 200 Bio-wheel not increase my Bio-load capacity by even a small margin?
Adding the second filter will have increased your tanks capacity to process ammonia - so that will either improve your water quality, or let you keep more fish.
What it doesn't do is remove the resulting Nitrate, so you still need to do the same water changes as before, or increase them if you add more fish.
Another plus with 2 filters, you have a backup in the tank in case a filter fails. The 2nd filter will at least keep your fish alive untill you can fix the problem.