I don't mind attraction specific shirts for some of the big rides in a park, but what i do want to see more of is POLO SHIRTS.
Nice, good quality. by all means go dye sublimation and have a really nice full colour thing like dreamworld, but don't use the same montage of ride photos that means the shirt is dated simply by referencing which rides are still running.
My preference (and things I wear almost weekly) is a nice wick-away (not heavy cotton or synthetic) polo, in a single, or two\three-toned colour scheme, with the park logo on, or in the position of, the breast pocket. MW and SW have these (although some are identical shirts designs in the same colours, just with a different logo, which is a bit of a cheap out.)
Polos in the 90's and 00's were widely available at parks all over - but in the 2010s, the collar seems to have disappeared to be replaced by simple crew neck t-shirts, which is disappointing.