Just some facts, from personal experience and Bulbapedia...
There was a new challenge after you defeated every gym, and the trainers in that challenge were always a bump stronger than the ones encountered on routes around that time.
He goes away after you complete his final challenge, obtainable after defeating the Elite Four. (This always gave me the sads)
It is the only way to obtain a tent for your secret base.
Each scroll's "code" is a compliment about the Trick Master.
But yeah, I always liked the Trick House, the EXP was nice and the puzzles enjoyable. But what's this about taking hours to finish a puzzle? C'mon guys, they weren't that hard!