Is just panning your percussion/hats parts all over the place a bad idea?
i think its a good idea as long as you dont have your hi-hat jump from hard left to hard right and back again this sound a bit wierd, unless this is the efx your going for.
Keeping bass/kick/snares dead central actually key in getting a good mix (and vinyl-isable?)
no. i think if these are your main elements in your track its best to have them more central, but it is always good to have some stereo efx's on them (reverb, chorus, ect.) you can have them a bit left or right as well.
Ccan you squeeze more juice out of a track if clashing freq.s are separated in the spectrum?
i think you mean separated in the stereo field. i think you can when you here some records the guitar is panned hard left and the piano is panned hard left, i think this is because if they where both center they would sound rubbish.
my main tip is do what sounds good for the track (no wronges or rights (or lefts(

))) make it sound good
and pan can also be used creativly ie sweep from left to right
and dont over do it avoid panning to hard left or right more is less in this case