I have alt characters and I enjoy creating them.
It saves me getting bored with 1 race and I can switch around and let certain ones build up rested exp and leve allowances and extra storage space.
Also one of the main reasons is I hate the way the fate system is currently and will not take part in the Zerg lemming style leveling that is going on in groups,I do them now and then but only solo.
It's a little bit annoying that you can not mail gear to your alts but I get around that by using the FC chest or market board.
I seem to see things differently the 2nd or even 3rd/4th time I level a character which is nice as this keeps the game flow interesting and less tedious.