One other thing. I am pretty sure that at high prices, bitcoin has historically been anything but stable. During extreme bubbles and crashes there is a lot of volatility.
Yep. That's another reason for my assumption that, in terms of its actual use as money (e.g., a in its guise as a medium of exchange on relatively short timescales) the best time for most people is during those boring lulls.
Its usage at other times is inherently speculative, regardless of the language people want to employ -- if you're accumulating because you think you'll be able to use it as money in a decade, that's an investment.