Well I decided that I did not wish to restrict the Power shot because I personally believe that It in itself is not to broken by itself however I have restricted the Dead aim so that you can not auto crit every time in a attack action (though even that is only a threat not an actual crit). I base it not being too broken off of telling blow which is a feat in PHBII to which allows you to add sneak damage to a crit hit. This happens only 1 time not by your multiplier so it is not quite as good as this power shot but power shot is 5 levels into a PrC not 1 feat . Also telling blow works even when sneak normally wouldn’t and power shot only happens when you sneak. (But now I will need to add a clause to keep power shot and telling blow from stacking)
I also checked with the simple Q&A guys in d20 gaming and they confirmed that my interpretation of hide in plane sight is proper and that you do not need cover or concealment as long as you fit the requirements of using hide in plane sight in this case be in natural terrain.