My dad owns star wars premium and Godzilla LE and I've got TMNT pro.
TMNT is way too hard for casual players and the scores are low (which bothers a lot of people). Still a very fun game, especially since it's one of the few you can play co-op.
Star Wars is also a very hard shooter and has a combo selection mechanic that would definitely go way over most casual players' heads. The theme would probably be enough for a casual player though.
Godzilla is a great fit. Easy enough shooter for a casual player and there's a lot of mini-modes you can activate by accident.

Word of caution, TMNT and Star Wars are pretty brutally hard shooters, especially TMNT.

Anyway, you should be able to sell your JP premium for 10-11k, which would get you close to two pros.

I own a JP premium and a pro (2 different locations). While the extras on the premium are cool, the game play is essentially the same so I think the pro JP is not really a compromise. And my family likes the cabinet art and translite better on the pro. Still just as fun as the premium for a lot less $. So if you get another JP in the future I don’t think you’ll be disappointed with the pro.

I have both TMNT and AIQ. They actually compliment each other nicely because they are so vastly different games. AIQ is wide open and a flowy shooter. TMNT has a full playfield with many different shots to make but TMNT is as many has said, a very difficult game.

Any update on what you finally decided? Between my son and I we have all three and all are great choices. I have over 20 games including most modern Sterns and the one I play the most by far is the Mandalorian premium. Also a tough game, but not as tough as Star wars and tmnt. As stated above, for a small collection, Godzilla is the one you want.

Thanks so much for the response. I definitely agree with everything that you have said. Turtles is definitely very challenging, but is an awesome game. Congrats!