If the scenes or models don't need it, don't hold on to it. And if you don't need it, don't hold on to it. Most likely with plugins you only need the updated version, so get rid of the old ones.
If you're just enjoying scenes just keep the ones you really like. I would say same with models but just check so you'll know what dependencies you should keep for them.
If you're creating scenes don't download every asset/environment you come across. Leave that for when you actually need it as you can get it from the hub by doing a search using key words.
Being afraid of deleting vars will have you with a 2tb vam folder faster than you can blink.