I think that if you are pugging for fun, then go for it. If Pugging is just a chore so you can roll on gear, then don't do it. I enjoy pugging a bit, so having 5 toons available makes it more enjoyable. I got into a bad pug, got saved to the instance after one boss, and then the raid fell apart. If i only had one toon, i would have been out of the whole place for a week. All I had to do was switch toons and start over. Now my 3 mages are doing much better dps, my priest is pumping out much stronger heals, and my tank can take a few more hits.

It all goes down to one fact. This is a video game. It's supposed to be fun. Do what you enjoy, 5boxing heroics, solo box raiding, multi multibox raid, PvP, etc etc.