You could just the same ask, why still play FF7 when there are newer games in which to play as the same characters?

It's nice to have a full chronicle of the characters in all of their incarnations, for whatever your reasons may be, from nostalgia to being a completionist.
That said, I actually have an old copy of Ehrgeiz too. In fact, their dynamic dungeon model in the side game is something I thought about quite a bit when considering possible venues for the AVALANCHE gameplay.

I've never tried looking at the data on the disc, though.