My position is that occasionally I might want a strobe, in which case I'd prefer two (and own them), but that most of the time I choose not to use them as I regard them as too bulky. The feeling that there is an inevitable progression from simple to complex (and expensive) pervades many activities, not just underwater photography, but out in the real world is often not applicable.
One of the few areas where I have been chasing technology is in land stills photography, where I've invested a fortune over the past year or so (well over $10k), and have more to spend. I bought myself an HD video camera & housing, but literally haven't touched it in over 6 months - it doesn't "grab" me. I haven't bought an underwater housing for a DSLR because I believe I can get good results (not as good, obviously) with a compact camera that almost fits in my pocket. In fact, when I go out I always carry a camera with me "just in case", but 95% of the time it's a compact in my pocket, not the $8k DSLR I bought a few months ago. That only gets an airing on special occasions.
Another area where I've aimed pretty high in the past is sound recording equipment, but that aspect of my life is currently dormant. As is the love of fast motorcycles - instead I bought one that goes quite slowly, is light to move around, and uses very little fuel, as being far more appropriate to my current needs. And there are other areas. I have decided what level to pitch my experience at, and then try to do the very best with that level of equipment. That's the philosophy I apply to underwater photography.