I'm not a great DI coach by any means. I've managed to build one DI team up from D- to B+ or so, though, so take this as you will, but...
I wouldn't worry about how high you can reach with a D- prestige. At DI, prestige differences mean a LOT more than at DII and DIII. Focus on lower DI guys with potential (and even some great DII guys) rather than trying to reach and get the high talent - you can get some of that later with better prestige.