The filter for region is a hot mess with the JP and PAL listings creating HUGE gaps between the NA consoles.  You have all the PAL and JP consoles batched together because of the names, but not the NA stuff.  We could REALLY use a top level drop down for the region, or just do with the NA what you have for all the PAL/JP and add "NA" or something in front of them so at least they're all together.

The chart on the My Collection page doesn't seem like it is tracking past prices for me, its only showing a visual chart from the date I began entering my collection. Is there a way to change that, is that a bug, or should this be a feature?

There should be a little number next to the current price of  a game in your collection that shows how much the game was when you added it to your collection so you can see exactly how much a specific game has gone up or down since you've had it.

Add an undo button if you accidentally hit remove all games while doing a lot calculator. 

Change currency displayed to CAD, USD, etc etc

The value and price tracking for the Game Boy SP is quite the mess for the AGS-101 models (from what I can tell). 

1. The graphite version is listed as a black variant so it isn't getting any data (and probably hard for collectors to find)
2. Pearl Blue and Pearl Pink have a hard time receiving new data so prices aren't up to date
3. Pearl Blue isn't receiving data for CIB condition.

This is just what I noticed but I'm sure there are more issues within the Game Boy SP variants/colors. If this is something I can work on to save you time let me know and I can try to correct it. I'm still getting used to the interface and what my abilities are in editing existing items. 

Thanks for this wonderful website! It is amazingly useful!