My Feedback thread: http://www.digitpress.com/forum/showthread.php?t=144938
My best guess looking back really is just that it's not so much rare, it's just fairly uncommon and sought by collectors and in turn highly sought even more by resellers, especially the predatory ones going for the highest margin possible for newbies who don't know better on one of their first scores. That game, Bubble Bobble 2, and many others for the longest time through the Funco period and after were like $20 bill titles if that. Funco you have to remember on quite a bit while still 'fair' priced were on the higher end a bit compared to other used shops that had to compete with the chain and private sellers too. I skipped on it back in the day, at times I wish I hadn't but I don't have an attachment to it, I did get Bubble Bobble Part 2 then w/the book for $20, back then paper and dust sleeves came with a game with no premium which I miss when that changed just a few years back. A thing to note with the game others said it is Capcom and stuff they put out in 1991 and after are high tier in the quality of audio, visual, and design which people really got into as they knew they had to compete with the 16bit trio in the market to get attention and the attention to detail in stuff like Gargoyle's Quest, disney sequels, and the rest show. I think it just is a mix of lower print run versus a Mario or a Mega Man, high quality, and the vicious cycle of reseller/buyer screwing each other using the last highest sold price to ask a couple bucks more.
I remember borrowing this game off my friend around the time it came out and liking it quite a bit. A shame that his mom ended up selling all of his old stuff years and years ago. Believe me, I tried calling him and asking if he still had any of it, lol.
I remember I passed this game up a few times in a local store back in like 2003 for $30 loose. It was pretty high compared to most other NES games. If I had known the price would shoot up only a couple years later, I'd have made it a priority over other games (same with EVO).