I've only been collecting for a few years now but I've learned a lot in that amount of time. Early on, I had a very common perspective for most casual collectors-- when I went looking for a copy of a game, whether just a cart or CIB, I wanted the first print run version.  This is my primary desire for games I'm collecting where I'm not looking to get a complete set.  However, after I started hunting down every original GB game, I found that there are some games that are either common or uncommon but their are certain variations that are extremely rare.

For the Game Boy, the market is still pretty niche.  I imagine there's probably no more than 15-20 of us looking for every North American cart variation of the GB line up.  Those aren't strong numbers and that would seem to suggest that this will continue to be niche and finding extremely rare copies might continue to be fun for those people who enjoy collecting for the sake of collecting, while not necessarily breaking the bank.

That said, the Game Boy is sort of the genesis of handheld cartridge gaming.  A lot of what we experience today in mobile/handheld gaming is thanks to the Game Boy.  The NES wasn't the first gaming system but it was the one that solidified console gaming as a mainstay for most of us.  I think the same could be said for the Game Boy from a mobile/handheld perspective.

I'm not trying to argue the they GB should "have it's day" or that one day GB games will be looked at like NES games but with time I think there's a good chance that people will start branching out into other areas of game collecting and start knit-picking what's available. Taking note of the history of the Game Boy, specifically, is still very important and could lend new collectors to join the scene, who might start looking for the more obscure stuff.

With that said, do you guys feel like rare variant hunting today might pay dividends in the future?  Generally, I'm not a for-profit collector, but I do frequently buy stuff that I feel is a good deal that I can leverage for future trades, or I can make a few extra bucks on that I'll sink back into the hobby.  The GB is my wheelhouse so if I'm going to hunt for extras and stuff to collect, it's the system I'd like to hunt for. 

You guys with more experience, what's your advicement on hunting down and hoarding the truly rare variants of very common to uncommon games that go for the same price as their common counterparts?  Is this a worthwhile endevour?

If you look at the more mature markets, it would seem that only a small proportion of variants tend to command significantly different/greater value. For example, some of the 5-screw NES games or grey cart N64 games. However, for the vast majority of variants there wouldn't appear to be much of an effect, they seem only to interest a relatively small number of collectors. For a set like the Game Boy, with what seems like more game variants than any other system, probably the effect on prices for variants would be even more subdued. I would imagine only the earliest print runs in excellent boxed condition would command a significant premium, and perhaps one or two other random ones because maybe they are insanely rare or have some sort of altered content.

Of course, no one knows for sure, and if you are having fun collecting them, that's the most important thing!  

The for profit collector should be looking for mint condition items they seem to always commend the most. My example that works well for this is my kid Dracula cib not an easy find to begin, now stack it was mint corners no surface scratches I sold it on feebay for 1200. I had tons of offers under that and it may increase in value overtime but the mint condition is what got me paid over market.

There are exceptions, but typically collectors only care about major variants (i.e. Zombies Ate my Neighbors alternate box art or MK3 PS1 Jewel Case version) that are rare and for desirable games. People don't really care about variants for 99% of sports games, for example.