Yes there is. It's like the classic burning of your ships once you've landed. Once you know there's no turning back, you have no option but to make things work by going forwards.
Besides, depending on the cost of the ring, and the length of the marriage, it would make you more likely to terminate the marriage over time as the cost of the ring gets amortized over the length of the marriage.
http://en.wikipedia.org/wiki/Engagement_ring#Legal_ownership
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.