When I change crank length, I do raise/lower the seat the same amount to keep the maximum leg extension the same. I am only 173 cm tall, but have a 84 cm inseam, and I have experimented with cranks as long as 180mm. I was really surprised that it was not a lot more difficult to spin the longer cranks, in fact they felt quite good. But I settled back to 175mm anyway, just because I didn't want to be getting to extreme or exotic with my equipment. I think you may be surprised that much of the "conventional wisdom" about crank length just doesn't hold true when you actually try them. Most studies end up claiming that length doesn't make much difference anyway, so it can't possibly be hurting too much to try them.
On the other hand, when I switched from speedplay pedals to Dura Ace, I should have raised my seat by a couple mm due to stack height differences, but I didn't. They seemed just fine without adjustment. So maybe I am just not all that sensitive to things.