Time is one thing you look for (like others have said). Best to take it down and rebuild it. Short of that look for seams coming undone, worn/loose bolts, what your grabing hold of to pull yourself up and things you can't see (the reason it needs to come down). Another biggy is what your using to get up there, it should be replaced too. I've heard of the tree spike rusting out, but I've never seen one with more than surface rust.

If you think the metal on the stand is still good add some more straps, Put as many more on as you care too, there cheap enough.