I use MRP in two ways, because I believe that by this two ways getting the most:
1. I buy TCredits - 1, while cost 126 MRP, but give me 102 VP (sales VP)
2. I buy another TripleClicks and SFI products with MRP while VP (VersaPoints) are awarded ONLY on purchases of TC Direct products. So, I buy what I want, pay with MRP, and get a VPs!
I hope it will help you in your decision how to spend MRP :)