perhaps wheels aren't the solution you're looking for. Maybe just carrying a strap that you can tie two bags together (maybe a 3 foot strap of webbing) may be ideal.

Most panniers have some place to attach these on top, if you tied one end of webbing to each you could sling the panniers over your shoulder easily and have one on the front of your body and one on the back. If they aren't heavy but they're awkward throw them around your neck.

Just a thought. I don't know if the added weight or trouble of casters would be worth the 100 foot walk you may have from the bike to the hotel room or shopping area, wherever. Then again I don't think the weight or risk of a kickstand is worth it either. : P

if you really wanted a simple carrier, I wonder if you could mod one of these to carry bags (distance measuring tool):
Then you'd only carry it when you wanted to, and you can get collapsible ones that are pretty lightweight.

Also, a side note: I would always tell the airliner that my unicycle was a specialized version of this to get away without paying for a bike fee. : )