Something I learned when using my MileagePlus Explorer miles is that you of course don't get reward miles on reward tickets...whereas if you book through the CUR portal you get miles.
I don't have a CSR or CSP but I'm thinking of opening it and cancelling my MileagePlus card before next year's annual fee. Or maybe I'll keep it. I dunno, the 2 lounge passes is kinda nice. I'm *A Gold but it's nice to have lounge access for domestic flights for one trip at Terminal C in EWR. Lol.