I totally agree, that you need to weigh all these cost/benefit comparisons. I would also add, that being non-union for as long as you can widens your network and makes you available for more work, period, even if it doesn't pay as much as an AEA contract might. The economy is not great, and theatre economies are even worse right now. You would be competing with out-of-work AEA SMs with much more experience and contacts than you have, and that will make it very diffcult to find a job, especially in a saturated market like NYC.
I am a huge advocate for the union, and at the same time I wouldn't have had the full-time PSM job that I've had for the last three years if I'd taken my card for a short-term gig when it was offered.
Just my two cents.