What to do with 10*/11* Units?

Have over 200 of these things cluttering up my storage. Since we’re only allowed to put up 30 items at a time in the store, any other good uses for these things, other than just discarding or selling them back for the Item shop?

swap them in for photon spheres really (5 units for 1 sphere), or if you have a ton of those selling, with one of my alts being a summoner I keep buying xp eggs. not really sure how the sphere market is cash wise.

Also spheres can be swapped for 75% expbooster