I'm an engineer, and while Ive no doubt I would love flying, I would miss engineering in the long run. I've no desire to fly for the airlines, and frankly I'm worried that I wouldn't be able to get back into engineering if I left it for a 12 year adsc (although that could be just a misconception of mine). The guard would let me combine two of my passions.
TPS would be heavenly exactly because it combines engineering and flight, but mostly because ultimately I want to get into spacecraft test and evaluation, and I feel that TPS would be the best avenue into that niche field. It would also help with NASA's astronaut selection boards, although I do realize it's a longshot and I'd be more than content with being a test pilot or flight test engineer in the aviation or space industries.
Those are the main motivators and, honestly, after a few years in industry I do think that I'd feel at home in the fast-pace and challenging environment of a flight test program.