You should, if space allows, keep your yoyos where they are and add three more.
Some ideas for a 55 or 75 (if you have the room, go with the 75. So much easier to aquascape).
1) Brackish Tank. Pair of violet gobies. A dozen bumblebee gobies. 3 male and 12 female sailfin mollies. If you can get the wild variety, they look so much better than anything in the fish store. Get the salinity around 1.008 with marine salt. Argonite sand (has to be sand). Google "brackish aquarium plants" for more ideas for planting, but your could do well to start with Vals along the back and sides, Pygmy Chain Sword in the foreground (to the sides), and java fern on at least three fair sided limestone rock caves (maybe with lengths for 3 to 5" diameter PVC pipe concealed beneath for support.) Also, make sure you get some honeycomb rock for the bumblebees to fiddle with, and put a couple of powerheads to keep the water stirred up so that the frozen food you'll need to feed the bumblebees will stir around.
2) Set up a low flow river manifold. Basically stick a spraybar through a filter sponge at one end of the tank, and run the tube under the gravel to a powerhead on the other side of the tank through a second spraybar. Then build the tank around a school of a dozen glass catfish. Maybe another dozen or two espi rasboras, and some of the more peaceful loaches, say 7 or so striped loaches or a dozen kuhlis.
2a) Same set up, but use 2 or 3 powerheads and an equal number of sponge filters at the far end of the tank. Stock with Giant Danios, Pearl Danios, Hillstream loaches, and Checkerboard Sand Loaches.
3) One I am seriously considering: 7 (in a 55, 13 in a 75) skunk loaches, and a big enough school of tiger barbs to defend against their depredations, say 15 or 30.
4) Rainbowfish. Set up a nice planted tank with a big school of boesmani or praecox or red irian or celebes or madagascar rainbowsfish. Plant the bejeezus out of it.
5) A pair, trio, or 5 moonlight gouramis, threadfin rainbows, albino cories, and albino bristlenose plecos. Call it Snow and Feathers.