I've had the MMF-5 for 4 years now. Definitely change the cart, other than that just leave it be. I think its not worth upgrading, the money is better spent towards a new table. I've tried lots of upgrades and found ultimately that the weaknesses of the table persist, and do so to a degree that its just not worth it.
A fine table for what its worth, but not worth upgrading in the long run.