I have definitely done this many times throughout my life...I'd beat an awesome game, but there would always be another I want right around the corner so i figure "eh, I beat it but now it'll just sit there collecting dust" and I always sold it or traded it in towards something else I wanted BUT many months down the line I wished I still had the game I sold in the first place to play. & now I feel like this towards certain older games that I don't even have a system to play them on, such as Shadow of the Colossus.
If only I kept every game I ever loved growing up, I'd have a tong of great games...unfortunately my younger self never thought I'd miss games in the long run. So here I am, at age 20. Regretting getting rid of 100's of awesome games. Games I may never see again. (I'm looking at you Conker's Bad Fur day!) -.-
Only game I have ever done this with is Marvel Ultimate Alliance 2. To make it worse I bought it three times. New twice and used once. Bought it new, completed it twice, traded it in. DLC comes out, bought it new again, got bored of it, traded it in...Missed playing it a few months later, bought it used....
Plan on buying RDR and Assassins Creed 3 again, once the dlc comes out for the latter and I have the dlc for the former, but never played it.
If you want to count rebuys of old games through collections, I've rebought many games. I have 4 copies of the original Sonic the Hedgehog (original cartridge, XBLA standalone release, Sonic Mega Collection Plus, Sonic Genesis Collection), 3 copies of Ristar (similar), and 2 copies of many other Genesis titles.
I have two copies of Age of Empires 2. Three of Morrowind (XBX, XBX GotY, PC GotY). Technically 3 copies of Tomb Raider Legend (XBX, 360, and the Tomb Raider Trilogy for PS3). I have 2 copies of Halo 2 and Gears 1, because a friend left them at my house and I didn't find them until years later, if that counts.
A couple of days ago I rebought Ninja Gaiden Black. It's the only physical game I've ever actually lost, because I lent it out to a family member who never returned it.