When i collect games i am all about completeness!? However w/ turbo grafx i tend to break that rule. Boxes are such a rarity on some games ebayers, which is really one of our main sources, only post their auctions with buy it now, as u were saying 1x or 2x higher than the game itself costs. Some games are up their w/ box only once every two months and their are so many good turbogames which are already fairly expensive i simply cannot wait to pay double for a box. I saw Neutopia II up there complete and it was the only one for a while for a buy it now of 109.99$. Cheaper complete ones have since surfaced. Dungeon Explorer II which doesn't have a cardboard box (to my knowledge) for a while the only complete one i saw was buy it now for around $250, since then two have surfaced and sold for significantly less.
So now that my rant is over i'm all about completenes for NES, SNES, GEN, etc, but w/ turbo grafx to find the game that you want complete in good condition takes a significant amount of money and it seems an even greater amount of time.