This is a pretty interesting thread, and I think I might fall under the hypothetical group of people that has been discussed in this thread that would be discouraged from playing if there was an entry fee.
I played my first Organized Play anything for the first time during the SPTs, because I figured "I've been collecting these cards for a long time, for the first time ever I'm actually within a reasonable driving distance to one of these tournaments, and I really like Platinum so I'm going to buy a booster box and see what I get."
I fully well knew that even though I felt pretty confident that I knew how to operate my Galactic deck, I probably wouldn't do that well facing someone else's maniac combo and I would probably have to resign to an autoloss a few times (such as if Mewtwo Lv.X came up, which he did) but I read the tournaments were simply meant to be fun and aside from buying more boosters of a single expansion than I otherwise would (being a casual collector who's simply in it more for the pretty pictures than anything else). But I went and I felt like I had a lot of fun and got a lot of experience, and am considering the practicality of taking a few hours of driving to OP events in the future.
It was really light hearted and I had a lot of fun, and I think at one point I intentionally held myself back because I could tell my winning the game wouldn't have meant as much as it would've to one of the people I was playing. I ended up going 2-4 that day but I wasn't really discouraged, and that Dragonair promo was pretty nifty and I randomly won a beach ball.
Aside fromthat initial larger than usual investment into a single expansion I didn't really feel that pressured to win, I figured I had probably spent a lot less than most other people there and there wasn't really any sense of 'well, I did put 10 dollars into this tournament, I'd better win as much as I can.'
I guess a semi-valid sentiment, however, is that a nominal five dollar fee encourages better prize support and most interesting promos for the winners. Someone might slam me on this and correct me, but I think the people who are winning large scale tournaments are usually the ones who've spent a lot more money than just a booster box of Platinum and a few packs of Legends Awakened on the game, so while 5 dollars to them is nominal and gets them a much better prize, I think I would personally feel like I'm handing an extra 5 dollars to someone I'm probably a bit jealous of, and I might be a bit bitter when I played against someone like that, potentially even becoming a bit hostile during the game and hold up the game arguing points I would probably let slip by otherwise.
I probably wouldn't have bought that Platinum booster box, and thus not attended SPT if there was an entry fee. Even when nominal, to me it would have broadcasted a sentiment of an entirely different gameplay atmosphere I probably would've had zero interest in.
