I hate when companies run these promotions. What they should do is allow you x number of tacos per day for as long as you live. That's tacos for life. Not $12,500 worth. Though, honestly, how long would it take you to go through these tacos.
There is one thing you guys aren't factoring in, inflation. Sure, it could last 40 years at today's prices, but in 10 years, tacos will likely be well over a $1. If you factor in a 3% inflation rate (on the low side historically) your likely chopping 10 years off of it. Not as much of an issue for the 4 year run.
All that being said, $12,000 worth of taco bell food for $600. I think I'd jump at that. I think I'd sell portions of it to aquaitences, maybe giving them 1/2 off taco bell food, get a few hundred back, and then buy a PS3 in a year or so when they are plentiful.