Perhaps I should have been more verbose. The point I was trying to make is that neither proposer is more likely to renege. Since they have both given away their 25k investment, it doesn't matter to either of them what the resale value is and thus it has no impact on their decisions. Unless it's assumed that you'll be combining assets upon marriage, which I hadn't taken into account in my original post.

Since you'll have to decline one of these proposals, one of them gets their ring back. Which one are you more likely to accept? All things equal, the 20k resale ring.