The "what if they wake me up to torture me" scenarios seem like wild catastrophizing to me - if someone has the political power and resources to develop special brain-torture gear, rez me, and keep me alive so they can torture me, they have the political power and resources to kidnap me and torture me with knives and fire as long as they want. It'd probably even be easier for them to do it to my physical body, right here and right now.

It sounds like the real worry is "what if I wake up in a dystopian future". And, of course, once you look at that, the expected value calculation is trivial. Consider the set of futures which have sufficiently-developed research and economy to systematize the operation of and systematically execute on rezzing random frozen brains. Consider the set of futures which have that property but are also dystopian enough to rez brains for the sole purpose of torturing them. Recall that these things are in tension; the kinds of irrationalities that lead a civilization to do that kind of thing will impair them in other ways, sometimes significantly - enmity from less-extreme polities, toxic culture leading to structural inefficiency, etc. You have to reach really far to find that region of the configuration space of possible future worlds.

So look at the expected values. Yes, being tortured for a while would suck. But being alive again, and possibly even biologically immortal, has the expected value of an entire new life. And the probabilities say that being rezzed is far more likely in a good future than a bad future. Literally every stage of the expected-value calculation says that being rezzed can be expected to be a win.