If you're moving him, it's entirely to a) free up the starting catcher spot for Jansen, get any assets you can for someone who isn't going to yield draft compensation after the year, and c) do a veteran player a favor by trading him to a contender where he could start (rather than back up a rookie on a rebuilding team).
If Houston offers a couple of low minors types who would rank 20-30 in our system and we have to eat up $15m, then do it. Why wouldn't you? Keeping Martin isn't going to help us get to the playoffs, and using him as a backup is a slap in the face to him. Not sure why people are so defensive about a trade like that. Don't give him away for s***, but a trade while eating some money is not a bad thing.