I actually found out about the Burrito Especial by asking at the Taco Bell near here. The person behind the counter told me about the creamy sauce, and told me (when I asked) that it was indeed dairy-based. So it sounds like it may not be that way at all TB's. I eat there semi-often, and just get the regular bean burrito instead of the Especial, minus cheese. Cheap, and yummy. The tostada is good too, just have them 86 the cheese.
FWIW, I tried the "Fresco" style one time. I thought it was totally yucky. Perhaps I'm a salsa snob, or perhaps their salsa was just gross that day but it was not anywhere as good as the regular bean burrito IMO.