Also remember that a points reservation doesn't earn points...which means that you'd also want to take into account your status, etc. For example, I've got the fee card and I'm Select Executive so the trade-off would be a loss of 7-8 points per dollar spent (partly offset by a gain of one point from the CC spend with Points.com). In a very literal sense, YMMV, but for me the loss of those earned points more or less eviscerates any advantage to buying the points that would've existed (since I'd be trading off what amounts to around a 20% rebate in the process). I would also frankly discount the value of the points as bought by about 10-20% to account for possible issues with the system (their failure to implement the 10% fee as indicated in the initial description), the fact that there are really no decent transfer partner options, and program change risk.
My threshold for buying points now would probably be a 50% bonus offer (which we saw once or twice in the past). At that point I would give it a good, hard look.