I do agree that Adele's music is less disposable than GaGa. Her album reminds me of Alanis Morrisette's "Jagged Little Pill" so much. Everyone had a copy of it. Everyone remembers it and loves the music, but as time went on, people started checking for her less and less.
If GaGa is able to pull bigger numbers next album or even sustain the numbers she has now, as an artist, she'll be remembered far more than Adele. I just don't see Adele trying to snatch wigs for the next 10 years. She screams novelty to me. Most of the talented ones are. They have a hard time living up to their big moment. Look at Lauryn, Alanis, Norah, etc.