I just redid a small section of one of my grids to change EXIT/XIS/CIGS/SSS to EDIT/DIP/CITY/SPY. This wasn't even a close call although all my entries in the EXIT version were valid. A good clean fill is going to wow an editor every time. A plethora of X's, Z's, Q's, J's and the like will buy you nothing but rejections if you pay too high a price for them. Similar advice applies regarding pangrams (grids which contain at least one occurence of every letter of the alphabet).
The reason for trying to work some high-Scrabble-count letters into your puzzle is so that you wind up with some *good* entries that aren't seen quite as often in puzzles as words with grid-friendly letters. But again, you constantly have to be aware of what trade-offs you're making. If you're compromising your fill at all, you should pass. At least that's my two cent's worth.