I don't think we'll ever buy anything but annual passes again. As mentioned above, we started out using them just at the first and last of the year. This time we will be there six weeks total (with the passes running out mid-week the sixth week).
I have a handicapped son and a husband with low tolerance for Disney. Some days we go over and just spend two or three hours, especially if the weather is marginal. If we were using day passes, I would stress out about how much it was costing for so little time. With the annual passes, there is less pressure to see everything commando style.
It really does make for a cheap vacation when you already have the passes. We stay in timeshares, so our lodging cost is low and we also cook in the rooms for several of our meals. I have to feed the kids wherever we are, so the only extra food expense is for dining out. We drive, so there is wear and tear on the van and related expenses, but usually not too bad (except for the time the transmission went out 150 miles from home).
If you can squeeze in at least two trips or one long one, then go for the passes IMHO.
Sheila