I have the same coach - on a Spartan. Tiffin's Powerglide is a great chassis but the biggest difference is seen when comparing a 40' Powerglide to a 40' Spartan. The Powerglide has better weight distribution and puts more weight up front. With the 42' tag axle chassis there isn't that much of a difference between them. They both ride and handle well. The powerglide does have a few benefits, such as the Vansco multiplex wiring system and handy remote air tank drain valves but those are minor changes. Also, Spartan has a 24/7/365 phone line for support. That can be handy if you have a question that they can answer and walk you through the problem to get it solved immediately. Tiffin is only available during normal business hours. Although, if it's serious, Coach Net will always be there for roadside assistance or towing with any chassis.
I wouldn't trade just for the chassis - unless you're looking for an excuse that is.
Quite frankly, if I had to trade right now it would be a tough decision and a very close call with no real loser in either direction.