The next thing I'd do, if I were you, is to sign up to eBay (if you're not already a member), and then search the site for "pro set music cards".
If you then put any auctions of the cards that you find into your eBay "watch list", you can see whether they sell, and how much people have been willing to pay for them.
Pro Set card sellers
I found a website here, which was selling a 1991 set of Pro Set Superstars music cards for £4.00 ($6.08 as of March 22 2013).
What are Pro Set music cards?
Pro Set is a Dallas-based company, started by a man called Ludwell Denny.
He began by selling NFL memorabilia, and Pro Set were the first to have an official association with a professional sports league.
The company released its first set of football cards in 1989, and later moved on to creating other types of cards, for sports such as hockey.
It also made cards based on subjects other than sport - as you can see below!
A wide range of cards - including Pro Set Desert Storm
Pro Set even released a set of cards called, "Desert Storm" in 1991, as you can see in the picture above.
These cards featured people who were involved in the Gulf War, along with pictures of some of the equipment used, but were criticised by some for allegedly being inaccurate in some of the details.
And finally - how Pro Set music cards were sold
You might enjoy this commercial for Pro Set music cards, which dates from the early 1990s.