This is quite tricky, as so much to balance.
My dc also have loads of stuff that doesn’t get played with, but some of it comes back into play, and has been used for years already.
Eg train set - we have lots, and most of it expensive Brio, BUT, we’ve had it 12+ years, and it still gets some use, so worth the money.
Same for marble run stuff - have stupidly expensive wooden one, with lots of different sets, but dd2 and ds still playing with it, and again have had it for 10+ years, so has worked out cost effective in the end.
Lego seems to be coming to the end of its massive popularity in this household, but does still get regular use, but only really by ds now (and me!)
And yes, things come in and out of ‘fashion’. Ds is not totally averse to still pulling out some of his dress up stuff, and dd2 occasionally will join him too if they are eg making an iMovie or similar (ds is 9, dd2 is 14!) - it depends how the mood takes them.
I would agree with not getting rid of things too early (wherever possible). I’ve had to keep loads of stuff lo Ner than I would have done anyway, as dd1 has a learning disability, and so still interested in the younger toys, but have noticed that dd2 and ds also benefit from being able to revisit and play with the stuff which would otherwise have already gone.