I would agree with that, but the GuitarPort has bass sounds in it as well.
I wouldn't say the TonePort is more *advanced* just more I/O options, it acts more as a mini-mixer than the GuitarPort does. Otherwise, if you pop open the box, bet ya dollars to dognuts, the D/A converters and main board are basically the same.
In anycase, I think both are a big step in the evolution of CPU+Guitar interfacing.