So far, I've just been elevating everything and then replacing the XM radios as needed with Force200.
I would say that around 75% of our XM radios are working fine, so they just get left alone unless problems show up, but the ones that keep dropping sessions constantly get replaced.
Each option has it's own upsides and downsides. Replacing everything with XW is probably going to be the least disruptive, but long term I'd rather have Force200s out there than elevated PowerBeams. The cost of a PowerBeam + elevate license is almost exactly the same as a Force200.
I think a big part of which is the best way to go comes down to how many XM radios are on an AP... and how many total radios, for that matter.