Multi-Tabling vs. Improving Your Game

[Bodhi]

Serious question: How many tables can you play at once and still improve your poker game? If 4 tables makes for a nice hourly rate, but prevents me from improving as much as I could, what should I do? I think I've gotten to the point where my initial learning phase (past year: .5/1->1/2->2/4->a little 3/6) is only sufficient for the 'small stakes' games when I multi-table, and I'd like to improve enough to beat these games handily. Should I eliminate a table or two? The increased aggression from good players, and donk aggression from bad players, makes me believe that I need to pay attention to every hand regardless of whether I'm in it or not (whereas I'm looking at another table when 4-tabling).
Anyone have a suggestion about something I haven't considered?