I got the bike - it seemed like too good a chance to pass up, and the reviews I found online were uniformly glowing. (As, for instance, this one: "My only negative comment about the bike was that I felt it was too comfortable"!)
It feels a hair small as currently set up, but I am thinking this is likely to be remedied by some adjustment of the seat, possibly new seat post - I'll take it in to Sid's Bikes in the next day or two for a tune-up and see what they can recommend for fit. Really it will be hundreds more I'll need to spend, that is the sad truth - definitely new tubes, maybe new tires, another helmet, saddlebag and contents (but there is a Cateye computer on it already, and it seems more functional than the one on my current bike, which has never worked for more than a day or two at a time!).
I think this was by far my most economical solution to the two-bike problem, though; I already have a soft bike case I bought last year, and I think I should be able to take it on Cayman Airways without getting charged separately. If it really does turn out that I can't get the fit right in a way that's problematic for riding long, I'll do my long rides on the spin bike and just make sure to do a weekly 2-3 hour ride outside on this one - I do think that for confidence and bike handling I need at least once a week on the roads, but as a novice I think that the indoor riding will serve me perfectly well in terms of fitness and I'm looking at a pretty slow bike split in any case!
A literary reader asked me in private correspondence whether $400 was cheap or expensive for a bicycle, as she had no feel for the price point in this realm of things, and I had to say that it was extraordinarily affordable (a new entry-level bike of suitable quality for the sort of training and racing I want to do would run around $1300 minimum, potentially closer to $1600, with the saddlebag/helmet-type expenses coming on top of that, and of course lots of the guys you see riding laps in Central Park are on bikes that cost $4000-6000 easily) - I directed her to the sale section (road and triathlon) at R&A Cycles for corroboration!
I have been eying that website quite a bit recently, but the fact is I am only just really getting comfortable riding a road bike: there is at least one more season of riding between me and a triathlon bike with twitchier handling, and the course at IMWI is rolling hills so a triathlon bike is for me at this stage actively contraindicated. If I can ever get my finances actually in whack, though, and improve my bike handling skills, it might be that there is a triathlon bike in my future....