DEN is always tough to find good MR deals. Typically I look to either EWR or SFO to find decent MR opportunities and either use one-way mileage awards or buy cheap F9 or WN positioning flights. Look for multi-city trips that go thru DEN on the last leg such as SFO-DEN-EWR. Another good city to look at as a jumping off point is PHX. Also check out EWR-SJU - that's always good for lots of miles with an immediate turn that's basically still a domestic flight.

I avoid pure domestic MRs now and only look for long hauls where the CPM makes sense factoring in the positioning flight and maybe an overnight hotel stay. Using points helps to keep costs down. Traveling mid-week is usually cheaper and easier to find upgrade space. My favorite MR was always DEN-EWR the night before, then EWR-HKG-SIN-SFO-DEN-EWR - back when UA had the HKG-SIN flights. I also like EWR-NRT-DEN timing wise but it's been hard finding good deals to Japan lately.