I "invest" in ntlds because I plan to develop some, and others I hope to sell. Yes, I'd say that its a gamble, but so is anything that is new. There isn't a business, product, service, or extension "in this case," that wasn't new at some point.
I think what's truly important, is making a wise choice when deciding how much you can afford to spend on these nTLDs and how much you can afford to lose. Because lets face it, they won't all be winners. IMO
To answer you question about dropping them, I plan on dropping the ones that don't make sense. Some would argue that none of them do, but that simply isn't true.