One thing to consider about the neilson system is that you only save 29 dollars per flat disc and 16 dollars per beveled disc over just buying more full discs from KMG for 83. That savings per disk will take a 9 non beveled discs or about 15 beveled discs to make up for the cost of the hub. I cant image it takes much more time to slide on a new disc on the motor arbor than to use the magnet system. The only bennefit I could see is that the individual neilson discs take up less space than a bunch of full size discs.
That has been my approach so far, but it does clatter your work space unless you come up with a storage solution.
I killed a 9" and a 12" disc sander and decided to go industrial. I was fortunate enough to find a 20" 2hp 3ph monster grinder for next to nothing because it had a bad switch. Using a VFD and a remote control navigated me past the need for a rotary switch and makes multi-speed a possibility. What ever you go with, remember that you can always rewire the motor and utilize a vfd. factorymation has the best prices on TECO FM 50's (though some don't like it due to its need for a clean box or nema 4x enclosure.)