Like lilsistar said, the gliderpedia page on diets is a great place to get info! A good, varied diet will increase the health of your glider (obviously lol) but also reduce boredom (you'd probably get bored eating the same exact thing every day, and so will your glider).
Are they tearing their toys apart with their hands or are they chewing them to death? Maybe it's boredom, but also some suggies are just chewers. Try getting them some edible branches to nibble on. Here's a list of glider safe trees:
www.glidercentral.net/ubbthreads/ubbthreads.php/topics/807750/Safe_Woods_and_Plant_Toxicity#Post807750
I've never tried it myself, but I know a few glider parents who put yogurt into a plastic straw, and then put the straw into one of those holey plastic ball things (for the life of me, I can't think of what they're called lol . . . wiffle ball maybe?). The gliders have to work to get the treat out. It keeps them busy, AND gives them something to chew (if your suggies do turn out to be chewers). Foraging toys in general are a great way to keep gliders entertained. (my girls pretty much ignore everything unless there's food involved ha)
Cheap toys are definitely a great way to go for destructive suggies. Lilsistar had some great ideas. I usually find a bunch of good stuff at the dollar store. Cheap cat toys (no catnip), little plastic toys to put in their ball pit, etc.
As for the salt lick, I wish I had more info for you! I'd say it's definitely good that you took it out. And if you're worried, pay extra attention and watch for any change in behavior/bathroom habits. If you notice anything worrisome, take them to the vet! Better safe than sorry, right?
I'm glad these gliders have you looking out for them! Good luck!