I also have a 20.5 Advantage and they are much shallower than a Spectra or Cheyenne. When my kids were younger I thought about doing the same thing. At that time Advantage was still in Anaheim and I talked to Harry about it. He said they would also lay some more glass in the bow area. The open bow boats dont have the benefit of the deck for rigidity, kind of like a car, hard top vs convertable. Never did cut the deck out and glad I didnt.
Very nice boat. You have a different seating than me. I have the engine cover all the way across the back with a bench in front of it.