To start off, I think Aquapolis is fine as-is. I don't think it's bad in any way. But, I feel like overall the system coulda been done a bit more elegantly.

My suggestion is that every Treasure Map should be able to open an Aquapolis portal, but at different spawn rates.

For example:
Leather: 15%
Goatskin: 20%
Toadskin: 25%
Boarskin: 30%
Peisteskin: 35%
Archaeoskin: 40%
Wyvernskin: 45%
Dragonskin: 50%
Unhidden: 50%
These numbers are just example, I don't really care about the actual results.

Why do this?
Right now, if it's not a Boarskin (Mariner Cloth for new glamour) or Dragonskin map, it's not worth your time to gather it. I think that's pretty silly, when there's a perfectly reasonable way to incorporate them into the system that made Dragonskin maps expensive and sought after.

This will probably get buried, but I'll feel better having posted my thoughts.