I have bought 3 engagement rings and all said and done I've spent probably $12-15,000 on the rings in total and I've ended up with a very beautiful 2 ct ring.
HOWEVER, there are times when my wife is having the ring repaired, cleaned, etc. when she wears a piece of her (i'll call it gaudy) fashion jewelry as a replacement and she gets more complements on that then she does the normal expensive ring. Also, I pay +/- $100 a year in insurance to cover the cost of the ring.
So, as I look at it in retrospect, I was in no way trying to buy my wife's love and I have no doubt that we'd still be happily married today if I bought her a $250 ring instead of one valued at $20,000. No one would ever know the difference and it would still be a symbol of my love to her. Plus, we could have put all that money towards a home, retirement, honeymoon, or something more realistic than one piece of jewelry.