I was out on my only Delta equipped bike this morning and didn't die.
They've gotten hate for their looks but I love them, and clearly so do many others. I've got a dozen bikes and the Delta's are the only brakes random people on the street approach me and ask what they are.
They epitomize the era of Italian form over function. Like the same era Campagnolo SGR pedals, which were over engineered, complicated, expensive, heavy and got widely slated in reviews....but they are still probably the most beautiful pedals ever in my opinion, and like the Delta's still expensive to buy today. People like pretty things. Beautiful versions of things seem to cost more than their fugly equivalents, in fact beautiful things car be worse than ugly things and still be forgiven their foibles, because, swoon.
I'm sure there are probably are some obscure and super rare and expensive brakes out there, but I don't know what they are. Are Delta's the most expensive old brakes around? Great if you they came on the bike you bought like mine, or if you ever want to sell them, not so great if you have to venture onto eBay for your first set.