Exonumia vs spot silver... spot will always win . The premium youre looking for is slim to none above spot. Perhasp a limited run numbered edition there may be some, but I would as most will only pay spot.
What's on the back? Sports ingots Limited edition of 2000. 2x spot would not be unrealistic to the end user.
Since there were only 2000 of these made, you may have gotten a bargain. There is one on EBay selling for $329, but we all know about EBay... https://www.ebay.com/itm/1973-Sport...HOME-RUN-KING-999-SILVER-ESTATE-/273874896278