Great topic.
I agree quite a bit if we focus on what pdas are doing today. You may not really need much more power. Lower price and power requirements would be really nice though! And I agree that the Treo650 is fantastic. Would more power help? I don't know. But a better and brighter screen and more memory would be nice. Faster hotsync would be nice. Wifi. Etc. It's great the way it is, but surely you have more "power" items that you'd like to see added.
There will always be power users that want the most in a handheld they can get. More is better, and more is never enough! That would be me, for example.
And it seems, fortunately, that there's still money to be made there. It's just not a great growth market like phones.
And I expect if we look further into the future, there are going to be a lot of reasons to use more power that we haven't thought much about already. I bet the device makers are already chomping at the bits for more power to do some of the things that are in the wings already. For example, looking ahead, voice recognition, handwriting recognition, AI processing of text, faster search, etc. are all expected future features that will get better and better with more processing power. I bet there are a lot of other things that will become useful also that we can't really even imagine, but they'll be neat and they'll require more powerful devices to do it.