I've known a few people who have only played one character in the game ever, and in my experience, they've done great-- all the money they make goes directly to them, they never have to redo rep runs, all the keys they collect never have to be collected again. If you are an altaholic, think about all the gear you've gotten across the board and all the time you've sunk into other characters-- people with just one toon get to put all that time and effort into just one character, and get to reap the rewards.
There is a lesson here, however, even for us altaholics. I've often found that if I really want to level up one of my alts, the switching just can't happen-- I have to choose one character and stick to it. All the money I earn stays with that character, and my only goals while online are for that character alone. And when I focus, and put effort into just one, that's when things actually get done. I, like many players, get bored easily-- if I had only one class ever, I would have had to give up on this game a while ago. But when it comes to earning gear and leveling fast, the best strategy I've found is to sit down, focus in, and play like you have only one character.