I used my old Diners Club (years ago) like the OP intended for the SPG card. That card, in its heyday was great - the points transferred into almost any other program out there at attractive rates, and no fees. Ironically, my big "blow out" transfer was at the end of the Westin Gold / start of SPG, when I needed the remaining DC points for the best award that Westin program ever had - the 500,000 point (equiv. to 100,000 Starpoints) trip for 2 - UA Business + 4 nights hotel in London or Paris - no taxes, fees, nothing. Just the points. Those were the days.