Is CPL an ideal filter for hiking, with all the scenery shots/ waterfall shots?
In a word, yes. (In a big way)
Is it a filter that could be left on the camera all the time for shooting other things that don't need 'polarizing?'?
Or is it a good idea to switch back to a UV filter when not needed?
You mention hiking. When Im hiking I normally replace my UV filter with my CPL, this way its marginally less weight, but more importantly something else that isnt going to break, putting it on and off in less than perfect conditions. Only downside is you cant just snap away, you need to align it before EVERY shot, which can get annoying.
For every day use though I put it on and off as desired.