I'm a 49yo commuter turned roadie now looking into getting into some mountain biking to keep things fresh/interesting. I've been doing some research and kicking some tires and pretty much have things narrowed down between a stumpjumper 29er evo ht (which I'd have to wait until july/aug for as the 2012s are sold out in my size) or a specialized epic comp 29 which my lbs does have in stock in my size ($2350 vs $3300 MSRP respectively). Though there's a $950 price difference, I suspect I could negotiate more off the epic than I could a brand new 2013 stumpy. I also don't know what changes, if any, might be made to the 2013 stumpy. I love how the 2012 looks, but, alas, they're gone. I like the idea of the simpler design (1x10 drivetrain, no rear susp), lighter weight, and better components (fork and rear derailler) on the stumpy. To me it looks better aesthetically (at least the 2012 did) and is a better value. That said, the epic is specialized's "race" mtb and supposedly is "faster" in most every area compared to the stumpy (according to the salesperson / what I can garner from my research). As a roadie, faster is better - at least that's my mindset. I also would likely get a better discount on the epic. I'm not interested in a used bike or an entry level bike. I'm not much of a mechanic and I suspect a used MTB would soon cost me as much if not more than a new one unless I got really lucky (and quite frankly, I wouldn't know what to look for - other than the obvious - to tell if it really was "only ridden 50 miles before I had an injury...blah, blah, blah" or in good shape). As for entry level, I suspect it'd likely collect more dust than dirt as I'd likely be unsatisfied and probably wouldn't ride it much. Any thoughts / opinions appreciated. Any advice on how to climb (pun intended) the learning curve for MTBing while having fun and not killing myself also appreciated.

Hardtail vs Dual (FSR) is a decision YOU have to make. But there are some items you have to consider. You're on the east coast so riding over roots is a fact of life. Dual suspension is way better at handling trails with root problems. Also, you're an older rider, (but I've still got you beat), and dual suspension is way more forgiving on the back and neck compared to a hardtail.
However, hardtails make you a better mountain biker because you have to pick your path more carefully. IMHO, similar level hardtails are faster, due to less weight to throw around. I have both a hardtail Stumpy and a dual sus Stumpy. On smoother trails, I take the hardtail and let it rip as much as I can. On a trail I'm not familiar with or a trail with lots of roots, rocks, logs etc. I take the dually to get through all that stuff.
As for a used bike, hard to say. I went used with both Stumpys, but I knew EXACTLY what I wanted. I think if I were in your situation, I'd stay with new.