tiny little things you could lose down a drain if you weren't careful, with discreet little price tags next to them saying things like ‘£4000’. I can't imagine what I'd have to be thinking to wear something worth that much on my finger

I get that too. I've never worn a ring worth more than a few hundred quid and I honestly wouldn't want to - while it would be wonderful for someone to like me enough that they wanted to demonstrate their adoration for me in insanely expensive stuff, I can't help thinking I'd be a bit paranoid about it on the grounds of how guilty I'd feel if said expensive stuff then got the stone knocked out while I was lugging musical equipment, or got dented or scratched by me faffing about with horses/bicycles/you name it.

Quite. Ideally you want to know that they love you so much they're prepared to spend £4000 on a ring, and then stop them short of actually doing so. Best of all possible worlds :-)