The Ring in LotR was an unusual item - for DND - in that it's power was related directly to the power of it's owner at that time and it had a will of it's own.
It would be modeled better by being an Artifact I think.
Do PCs /really/ need something to spend their gold on?
Yes, I agree, but the problem is more serious. It actually just doesn't make sense that the sale price is 20% for an item that does not deteriorate in value!The idea is good - the sale price thing isn't. It's completely counter to common sense that common items have the highest disparity between selling and buying price. The more common the item, the less the disparity between buying and selling an item should be.
Finding this price too high, my character stands outside the merchant's shop with a sign saying "I buy +1 sword for 100 gp!". Since +1 swords are common and everyone who tries to sell only gets 72 gp, I will soon find a seller at that price!!
How many +1 swords do you really think are being sold? If you have to stand outside that store for four months to get your sale, that's a net loss.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.