***BEFORE ATTEMPTING THIS, CHECK COMMENTS IF SOMEONE ELSE HAS CONFIRMED THAT THIS ACTUALLY WORKS, OTHERWISE I WILL PERSONALLY COMMENT ON RESULTS IF NONE ARE PROVIDED BY THE TIME I FINISH TESTING THIS***
Okay so I've separated islands to areas of symmetry and joined those together. The process follows. Identify points of symmetry within the island. Select the vertex's you would like to separate from the island. Overlay those symmetrical islands to take up half the space of a regular island. (Press Y to separate a group of vertices from an island)
The only expenses to this method is that if you do it to an island too many times i fear that a loss of detail will exist in repetition of symmetrical islands in the final project, I would limit myself to only 2 maximum symmetrical overlaps to prevent this but i personally prefer one so it looks like i actually put effort into my work with more detail in the painting. The next expense is that it is more time consuming, I've spent a good 2-3 hours reducing my islands to a very, very small amount, i know it's a bit of waste of time so i would only recommend using the "symmetrical overlap" method when working on projects that are larger than the average indie game. Personally I like to practice this in all assets now but whatever floats your boat :).