Oh yeah it's definitely a hit and miss market. I've got a few signed things here but I'm not keeping them because could be worth money, (they probably aren't anyway) but I certainly wouldn't be buying something like cards or figurines or the like from a company that's producing 'memorabilia' with the hope of being rich one day.
My uncle used to sell photographs of tennis players and golfers, in game action shots framed with the game scorecard under the photo. The ones with the original card were one of a kind but he also got authorisation to copy x amount and make them numbered collections. Everything was done with the players consent and he did pay a lot to get the access he did but he charged a fucking fortune for the pictures too. They are collectable to the right fan but it's not like they ones with the copied scorecard will ever really go up in value, the original cards might but again only to the right collector.