Building value is the same as "investing" in this sense. Investing in high-quality cards of a Hall of Famer like Tony Gwynn is the trading cards equivalent of investing in a stable value fund in your 401(k) plan, without the added insurance protection that a stable value fund gives.
Your ceiling on Gwynn cards has nearly been reached. His career is over and he has already passed away. There isn't anything he can do physically that is going to make the demand for his currently available cards skyrocket. The best case scenario is that you get a 1/1 card that you re-sell and a few Gwynn super-collectors get into a bidding war over it. Mostly, you're probably looking at a few extra bucks if you decide to re-sell a high-quality card, maybe a 1% increase in value. However, as we get further and further away from his career, your pool of Gwynn collectors will dwindle, as those who saw him play or were a fan leave the hobby for one reason or another, and newer collectors have less of a connection to him.
The other possibility is that something is revealed that causes his card values to plummet, which then leaves you holding an empty bag (by all accounts, Gwynn was a lovely man and I highly doubt that anything earth-shattering would be revealed, but it could happen). For what its worth, you could take the name "Kirby Puckett" and have this same conversation.
Point for part one: you're setting yourself up for disappointment if you think that buying high-quality Tony Gwynn cards is going to lead to a future windfall (or extraordinary increase in value).
I am going to make a suggestion that is probably going to come across as rude, but please take it as simply as advice based on my observations: do some research. Your first ever forum post on here was about buying a binder of all Tony Gwynn cards ever made. This suggests to me that you are relatively new to the hobby, with little knowledge of how it works and what all goes into it. And that's fine - we were all there at one time. But jumping in head first like this is the mistake that a lot of people have made, both in the late 1980s/early 1990s, and more recently during the Pandemic.
Check out the crash in the 1990s. Look at the current market conditions. Understand what is out there, understand the history of trading cards, and understand the general direction that we are heading. Feel free to ask questions about it. Really dig in and gain an understanding of the hobby world. Then decide if you really want to continue to acquire trading cards for future values.
Final thing: many other members have already told you in various posts to collect how you want. That's the best advice I've heard regarding anything, ever. Collecting how you want would include, however, lessening the amount of validation that you look for from others on this site. Your posts seem to come across as you either looking for feedback that you're collecting the "right way", or to make a case as to why others are collecting for the wrong reasons or the wrong way.
Collect what you want, how you want, for whatever reasons you want. Just make sure you understand the possible consequences of your collecting habits.
Nec Aspera Terrent
I'll never quit collecting entirely, but I am downsizing. Check out my COMC store and help me thin out what I don't want so I can buy cards that I do want. See something you like? Send me a message on here, and we can knock the price down quite a bit. I'll even take a bit of a loss if it means getting you a card you really want.