Dude, those older Pokemon must be so bored and lonely. I miss them, too. So yeah, that would be cool.
From time to time is the key here, maybe for a short arc, maybe for helping his current Pokémon, I think there should have a balance between his older mons and his newer ones, and while I disliked him bringing them to Johto, and then getting worse by not even using them, it just seemed like wasted potential for new captures.
Not for regular use, no, because then the newbies wouldn't get as much screentime! I felt similar to this in Johto, with Squirtle (while he was there) and Bulbasaur taking up a lot of the limelight (even though I love them both to death). I would prefer if they were brought back in a "Bulbasaur, the Ambassador!" type of episode, where Tracey would trade for the day depending on what the situation was.