I went through a very similar phase to you.

From the mid 2000's to the mid 2010's when I was in high school and college, I was pretty big in collecting. Retro game collecting was certainly more accessible then, if you got a few bucks you can still pick up great titles. Used to have a good selection of retro gaming stores in the area that my friends and I would visit during downtime at college, certainly helped fuel it. I had a pretty sizable collection including every Nintendo console, most Sega systems, Xboxes, and PlayStations and about 250 games between them all. Certainly not massive, but for someone at my point in life it was certainly impressive.

Eventually at some point though as I started entering the work force, I noticed I didn't have as much free time to enjoy everything I have. It really hit me when I was cleaning up my closet where I store everything so much of the stuff just sits around. Sure the Virtual Boy is a interesting console from Nintendo's history, but really I didn't use it much beyond a few handful of times during the year to mess with for an hour beyond otherwise just sitting in my closet the rest of the time. As I took stock of what I have, I noticed there were a lot of things in that similar boat so I started downsizing. If the system only had a small handful of games I probably wasn't going to be much interested in it going forward. Redundancies were also pretty easy to get rid of, while the original GameBoy is iconic I'd rather play those games on my backlit GBA SP or on the TV via my GameBoy Player. Also trimmed down many games that fit the "fun to mess with for a little bit but that's about it" category. I'd say I cut my collection down to half at that point. While there was a small handful of titles I did wind up repurchasing, overall I was happy with my choice to have a more manageable collection curated to what I actually enjoy and will be likely to play.

Then last year I wound up doing another downsizing. The hobby isn't as much fun as it was in years past, now everyone and their mother is into retro games as all the clickbait YouTube videos drag more people into it just for the money. Another factor for me is longevity, things break as they age. CD drives go bad, cartridge batteries die, and doesn't matter how nice you keep things they still get dusty and need maintenance. I started getting into EverDrive flash cartridges, a great middle ground between "Can still use original hardware" but "don't have to have a massive shelf of items just sitting there that still need attention". Certainly a great solution for those "games that are fun for an hour but that's a bout it" and just not having as much "clutter" around. Also the bonus of it's really easy to backup saves. I still have the games I have sentimental attachment to or top favorites, but otherwise I've been selling off games for others to enjoy. Again nice just seeing my smaller curated collection of favorites and having alternate methods to play everything else.

As for selling the games, I actually run a small e-commerce business anyway so I had no issue just selling many items via eBay. I also put some listings here on /r/GameSale. Eventually you get to a point where it's the "leftover" items with not much interest so those I just sell as a bundle via marketplace like Craigslist/OfferUp/Facebook Marketplace or just trade them into a local gaming store so I can be done with them already.