I think WE is a lot like some other ratings for players - its value is relative to what you want a player to become and how fast you want him to get there.
This last cycle I recruited a guy with 13 WE. His ATH, SPD, and DEF were all upper-60s to 70s already which is why I wanted him so much (I desperately needed a defensive upgrade). I accepted his flaws, including his low WE, because he was already better defensively than anyone else on my team. So It's not like a low WE was going to make him useless for me.
In most other cases, I subscribe to "the higher, the better" but WE must always be factored into Potential, too - a guy with 90 WE probably isn't going to become a 30ppg scorer if his LP or PER are under 10 with low/low potential, no matter how hard he works.