Well, I finally ate there today. I had two Carne Asada tacos and one Pastor (from the spit). I must agree with and thank David for the rec. These tacos were very good. The place was packed with Mexican diners, and the home-cooked meals looked fantastic. I've already talked to a good friend and we'll be going down soon for a good dinner.
While on the way over to E&L market, I also stopped in at Taqueria Tapatia (On Vernor just east of Clark) and tried the Carne Asada. It was a little bigger than Lupita's, and dare I say with as much flavor or maybe even more. The only slight problem was that there was quite a bit of fat and gristle on them, which isn't my cup of tea. I also much preferred the tortillas at Lupita's.
For those reasons, plus the fact that the dinner plates looked so great at Lupita's, that'll definitely be the one out of the two that I go back to first, and I have a feeling probably more often in the future.
Oh and by the way, I just got back from L.A., where I went on a pretty exhaustive search for great tacos and found them in droves! So the fact that I could enjoy any tacos from around here at all is testimony to their high quality.
Thanks again for the rec, David.