Thanks and I actually do have more stuff to add and responses to your points that you brought up (all of them good btw):
1) Real versus Fake jerseys: This has and always will exist. It really depends on the source. Luckily the Devils and 7 other NHL teams are right now with Meigray (Devils have been since 2003) and they are the most reliable source for game worn jerseys. They have contracts with the teams they deal with so they get it directly from them and have the whole serial # tags and population reports to prove authenticity. Rangers have Steiner who had a rocky start, but they have gotten better over time. I believe the Rangers now use 5 sets of home and aways plus 2 sets of Heritage jerseys plus a new set for every round of playoffs. Therefore in a season if they reach the finals each full time player will wear up to 22 different jerseys. That's a ton and that is at the request of Steiner. This is actually an improvement over when Steiner initially took over the Rangers program from Meigray back in 2010 when stories flew that you would contact a rep at Steiner, tell him you want a specific jersey you wanted with what kind of wear, and the rep would make it happen. It wouldn't be a fake jersey, but it would be worn in a limited amount of games or in certain situations thus leading to some players having tons and some players with scare amount of jerseys for a year.
Fanatics is now getting into the game as they handle St. Louis' gamers as well as special events (WC, CC, SS, etc) and selling through NHL Auctions. Their stuff is legit but they are struggling with tracking their jersey and when they are used, so they are taking a lot of heat now from collectors about this. Most fans who bid on this are oblivious (or just don't care) and just take Fanatics word for this when they were used.
2) Photomatching: Seems to be a lost art these days with dealers putting set tags in and people feeling safe that their jerseys are coming from one of the big companies like Steiner and Fanatics. Admittedly it is hard when you have single game and single period worn jerseys to match to jerseys with no marks, but it is always nice to get a good match.
3) Overproduction of jerseys: I partially answered it in response 1, but it depends on the team. Devils wear 3 sets plus whatever specialty jerseys they wear, so it's not that bad. Other teams like Anaheim who have Beckett as their dealer seemingly wear a new jersey every other game, so they have a ton out there. On the other hand teams like Detroit wear 1 set in the season and 1 in the playoffs. That's it. They also only sell their jerseys in a sale at a small store outside of Detroit once a year and that's it.
4) Cards: Cards are a waste of time and money IMO, but I can get why people are into it. It's an old tradition to collect them, but I would never see them as an investment like my game worn collection (even though I would argue gamers, if done right, can at least hold their value much better). Plus with the overproduction of them since the early 90's card makers have to play games and force limited edition cards to raise value. They put gimmicky stuff in cards like real diamonds and swatches of "game used" material when they have been caught in the past putting in fake stuff.
5) Autographs: Another hobby that shouldn't be used as an investment. The only ones making money off of these are the original sellers like Steiner who obtained the autograph in the first place. I see the same people at Devils signings getting autographs of the same player that I know they have tons of autographs already for. It is 100% their business and how they want to spend their money, but my personal rule of thumb is that if I don't think I will ever look at it again or display it, I am not getting it autographed. These days I only go to autograph signings to get a photomatch of one of my jerseys signed by that player.