For me, there is also the added risk that to leave a tt job in my field is essentially saying goodbye to the tenure track more broadly. What if, two years from now, a great tt job came up in the city where I live, and my cv shows that I left a tt job for a renewable term position? Why should they consider hiring me back for a tt job? There's also that concern.
Yes, I think this point is crucial. It
might make a certain amount of sense for you to leave your current TT job and take a renewable position if the new job allowed you to focus upon your research--and if you were going to go back on the market for a TT position within a year or two (and if you are prepared to move for a new job). Leaving a job with a very heavy teaching and service load and using the new position to boost your productivity in a visible way so you could get a new and more research-focused job would certainly be a risk, but it could also look like a reasonable career move. Leaving a job with a heavy teaching load for another one with a heavy teaching load, and then having to take on additional consulting work, with the effect that your research productivity does not improve measurably, however, is not going to do a thing for you as a candidate for future TT jobs.