Do you have any idea of the max amps you are able to see with the current arangement? Are you getting 5 amps? 10 amps?
The max your panels are rated for would be 360 watts or 30 amps.
However, you may or may not see the max current, especially if you have sub-optimal conditions in the winter.
Anyway, knowing the emperical data of what you are getting currently should help with the decision.
MPPT controllers usually are only rated to provide benefits at over 100 watts (8 amps or so). However, if you have enough power, they may give you significant benefit, and thus cost savings.
--- CK ---