Impressive collection to say the least. I really like that you have the older games from the Master System era, as Sonic 1 MS is how it all began for me (I'm guessing 1991), and really wish I had kept all of my Sega MS and GG stuff.
Not sure if I could have a collection like that though. Firstly, I think the wife would have a problem with me spending the money, second, no space in our small apartment and three, being a minimalist and someone used to having no choice but to sell stuff often in the past, I would be too tempted to sell off stuff if I saw that the value went way higher than what I paid for it.
I was thinking about doing my own Sonic Team collecting many years back. Right from Sonic 1, right up until Billy Hatcher. It was after that game that I think the development studio fell from grace - where their creativity started to falter. But, the reasons above prevented me from doing that collecting, long term. Also, not sure I'd buy multiple versions of the same game, as they wouldn't get used.
Right now, I'm looking to just collect my favourite Sonic titles, in their best versions, along with the odd Sonic trinket that I find on Amazon. I have a few keychains, a rail card holder, and thinking to get a plushie for my son, or a figurine of Sonic to put on my desk. But most of the figurines are based off of his newer designs, or are of bad quality, when I'd really like one that was reminiscent of Sonic 1 or Sonic CD.
One question I do have is; do you have any fond memories related to any of the memorabilia that you hold? Back in the UK, I still have my original Sonic and tails cuddly toys somewhere. I've had them since around 1994, I think, and a lot of memories taking them with me places, etc.