A few thoughts:

As soon as I saw that mirror, I thought ugh, I don't want any part of that. I spent too much thought and effort to get my party the way I like it, I don't need no steenking respec. And even for exploiting purposes, it's too much hassle to keep going back and forth. Also, if you try out new builds with respec, you completely miss Act 1. I would want to see how the new build fares there as well.