I was faced with the exact situation you describe. As a result of following FT threads, I set up a Hilton Fund Mutual account and except for our AA miles (not in their program at the time), transferred most of our ODDS and ENDS flier miles from various airlines to Hilton Honors.
Then transferred just enough air miles back to TWA for 2 free tickets which we have since used.
Even though it works out that you pay approximately 3 old good miles for 1 useable new mile, its worth it.(5000 air miles =10000 HH:: 10000 HH=1500 air miles).
Better to have a useable award than have to pay for a ticket and still have odd old miles floating around.