I have a couple of thoughts.
1.) Super 4x4 & 5x5: As stated above, it solve like a regular 5x5, solve like a super and regular 3x3, and of course 5x5's can't solve like 4x4's you need a super 4x4.
A 6x6x6 can simulate a 2x2x2, 3x3x3, 4x4x4 and 5x5x5. I'm not sure if super stickers are available for one or not but if they are they'd make the 6x6x6 even more versatile.
2.) Circle 4x4 I & III: Version III can solve like version II if you ignore the circle corner pieces and also can solve like a Circle 3x3.
The Crazy III is a superset of the crazy I so you only need the III.
9.) Square-2: Can be solved like a square-1
It would be hard to use a Square-2 to simulate a Square-1.
10.) Bauhinia dodecahedron: harder than a dino and rex cube but can be reduced to both.
You can't reduce it to either. The Dino Dodecahedron offers very little more than the Rex Dodecahedron so skip it but you can't get the Rex Cube experience on the Rex Dodecahedron.
I'd add the Dayan Gem (probably II and III) to the list as well as a Megaminx.