I've just started looking into sports card grading after getting some video games graded last month. Most of what I have is from the "junk wax era" which includes your 1990 Bowman set. I did sell a factory sealed 1990 Bowman set for $11 on eBay two years ago. I recently sold a sealed 1990 Score set for $9 and most of these sets cost about $20 back when they were new. Card sets are also usually heavy so shipping can be high but it's better than tossing them in the garbage. This week I went to list an opened 1986 Sportsflics (it is spelled without a "K") set on eBay but then held off because of grading. The small 75-card set sells for around $15 which isn't too bad but there are a few recent sales of cards from the set selling for $25-40 graded. Therefore, if I were to get two of the cards graded and sell them for $20 each I'd have a profit of what the set alone would sell for. I never know what to make of this and most sales are probably isolated cases as you just have to find the right buyer. Of course, there are also the people trying to get a ridiculous amount for some of the Sportsflics cards, like $300 for a single graded card from that set, but then maybe it's not ridiculous if someone actually pays it? I saw in other recent eBay sales a Frank Thomas Score rookie card typically sells for $1-2 but someone got $70 for a graded card (if these listed sales are genuine). I didn't think anything from the late '80s and most of the '90s would command that kind of price, even graded. I really don't like to break up sets either but selling the individual cards, even ungraded, is probably the better move financially and it's easier to ship a single card. However, it's also time consuming to do that so it may not be worth it in that regard.
I stopped collecting during the '90s so I don't know a lot about newer sets. A quick search shows that the 2011 set with Mantle on the box does sell for more than $100. From what I've read, MLB tried to reduce the market saturation at one point and stopped licensing to multiple companies so I think only Topps makes official baseball cards now. Many of the others have since gone out of business, like Score, Fleer, Donruss, etc. Upper Deck is still around making cards for some other sports and non-sports cards.
