a critter 3 cage? i'm not familair with the name. perhaps posting a pic of the cage incase others have the same cage but know its name. a lot of people get cages second hand from classifieds or ebay so they may have been advertised as the wrong thing too. just a thought, you might get more replies that way.
depending on where you live some cages are not as well advertised or as easily available making it les well known.
that being said i would have a ball decorating that cage. i'd line the platforms with fabric. put in a few igloos and hide holes. have a couple of hamster balls hungup in the corners, a few ferret corner trays as well. i'd probably take out the half platform at the top to make room for some dryer hose tubing, hammocks and other toys from the dollar store like hanging flower pots filled with rags or dirt to dig in. i'd probably also leave the bottom tray bare of toys so they have more room to romp there while above i'd put the igloos for them tp hide and cuddle in. i'd probably put the wheel in top section as well. i'd probaby replace the ramps for ropes or tree branches so they would be encouraged to climb more.
i love rearranging toys and adding on to my cage. its so fun for me to do just that and so rewarding when the rats actually use the toys.