I don't avoid them per se, but I rarely run them, either. It's more to do with my philosophy of the planes, than it is finding it too hard to run.
I believe that the planes of existance should be extremely powerful places that mortals should tread carefully, and the idea of having lower-level adventurers travel there grates against my feeling of what the planes should be. Since we rarely run high-level games, planar plots rarely come up.
When they do, I feel they should be impressive places to travel to, full of weird things and some tough opposition, a place that the players have their characters venture into and think, "Oh, boy, we've made it in the big leagues now!"
It was always one of the big turn-offs for me when Planescape introduced many means for low-level adventurers to survive and prosper in the multiverse; Sigil, while a cool concept, basically placed Modern-Day New York in the middle of the 1800's Louisiana Purchase, and it grates against my feeling of what the planes should be. When I rarely run a planar game, I want it to be skin-of-their teeth, and necessary, rather than the setting for a politically-oriented adventure. There may be occasional outposts of safety, but none that are easy to come by.