Sure have - the answer is inflation 
The other thing to consider is that your way of thinking has become very popular since the beginning of this financial collapse, meaning that the demand for gold is extremely high. While I agree that paper is essentially meaningless from a fundamental standpoint, it does have an intrinsic value, which does in time become devalued as more of it becomes available. Gold is a commodity that actually has no real value. Itās full worth is based on perception and supply and demand. Gold canāt house you, feed you or love you, but unlike paper money, it doesnāt necessarily become devalued over time. I think that since demand is so high, gold prices will come down (and may come down hard). The value of the USD will also come down. At this point, I actually like the stock market as the best area to invest in, followed closely by real estate in choice areas. We may see another trough in the market, but we should see way more peaks than troughs in the next 5 years. Buy low, sell high 
Thundercats and other toys ARE tangible products with intrinsic and extrinsic value. Granted you canāt eat them or use them for much besides looking at them and in a true recession/depression no one cares about buying these things, but I think long term if you were to carefully buy $10,000 in premium Thundercats or other 80ās toys (Transformers really arenāt at rock bottom prices but theyāve stood the test of time, He-Man, GI Joe, and vintage Star Wars can all be had at the lowest prices in years) at the prices in this market and not touch them for 5 years you would find a higher yield than stocks or gold. Just my opinion. Iām not going to do this because I want a better house down the road so I need to save my money for that but Iām trying to buy everything I donāt have while the getting is good.
P.S. If my count is right I account for six of those purchases and 1 sale Kyle! lol I agree that AFA graded and 8 backs should have different prices, and to be even pickier maybe foreign vs U.S. releases because those things do make a difference.
As far as the 8 backs. I know 100% that in January an AFA 80 MOC 8 back Lion-O sold for $799.00. The item number was 220332165913 (had it bookmarked). It no longer shows up though on eBay.
An AFA MOC 8 back Mummra sold at the same time but I do not recall for how much.
I think what I am gonna do is instead of bookmark those high selling eBay listings for reference, I am going to take a screen capture. That way even when eBay does no longer provide the listing details, we still have a screen shot (proof) of the listing. More importantly, how much it sold for and the date of sale.
I kinda just zipped through the completed listings really quick, so I didnāt differentiate between 8-back and card variations.