Its not always about the money, like the OP said, sometimes the Journey. Being a distributor, its very easy for me to "come across" just about any title i want. Although i have had some of the rarest games, its actually always been about the hunt for me. Once i get something unique, take it to a show, then move it along.
But my prized game is my Data East GnR, And not because of its value, its actually probably one of the middle of the road games pricewise. But the damn sentimental value makes it priceless. I went through a nasty divorce 20 years ago, and lost my entire collection. Lawyer fees ate it all up. The one game that i missed was the GnR, so 5 years later, I was in the town of the people that bought it from me. I just randomly stopped and knocked on their door. I asked if there was any chance that i could buy my game back (they knew the reason i sold it years earlier) They agreed to sell it back to me, of course at a higher price, lol. So i have the same game that i had twenty years ago, and I bought the game back.