I've read several Crowley biographies and he certainly didn't sound like a particularly pleasant person. Nevertheless, he certainly did produce deep and meaningful works in the field and his influence on the contemporary occult world is significant. I'm not a Crowley apologist, but I do have respect for the fruits of his labors. Now, Truth is a different matter. Is there a specific, universal Truth that is the end all of everything? I doubt it. So, in a sense, any personal development moves one closer to truth, just as a good education moves one closer to knowledge (but not necessarily wisdom!).
As far as power, I will concede that perhaps yes, I do wish to increase power over myself, which in turn will increase power over the outside world. But I don't think of this as a force with which to rule or control others, but as a force with which to better rule and control myself. Again, Power is a word with many shades of meaning. And I've certainly worked with introspection and meditation, and still do, but for me, I've found that outside perspectives have been beneficial.
Finally, I do agree than one must always be on guard for deception and ulterior motives, be in in an occult group, an educational institution, the workplace or any other situation where human beings are working together.