I'd put it towards a new cat tree. Ours is 17 years old, and the last time I replaced the elements (i.e, shelves and base) was 4 years ago. There seems to be a bit more of a "wobble" to it recently.
Of course they don't. They have a pretty fantastic life. They know how fortunate they are.
They sound really cosy! I think I'd like to curl up in one of those and take a nap myself.
Cat furniture is crazy expensive, isn't it? I build my own these days. It's not as pretty as the stuff you can buy, but the cats don't seem to care.