Maybe I shouldn't answer this, as I'm hardly a frequent flyer, but here are my thoughts. Where would you want to go if not guided by miles? At the same time, what appealing destination offers the best standard-price/miles ratio?

For me, Buenos Aires was a good choice in this respect (although if you lucked into something like that recent deal, it might not be). I both wanted to go there, and the price/miles ratio was very favorable. (Note: I'm using Aeroplan instead of MileagePlus for this, but I think the example still holds.)