I've only played a handful of games on both of these. I do think the prem or le of JP is one of the best pinball games quite possibly ever. Love so much with that game(except the theme... I love dinos just not the Jpark movies). The pro is still an amazing game. Just I mean, that t-rex head on the Prem is the best damn toy ever(or at least one of the very best. Top 5 all time).
Love the rules, animations... And an amazing layout. I don't think you'd get bored playing the JP pro. Just so much amazing stuff to do on that game.

As for the Simpsons Pinball Party. That game is really fun. I prefer the simpsons as a theme over JPark. Its got a nice sense of humor and a good amount of modes. I think you're right about finishing all on this game. As even Bowen had trouble collecting all of Cletus' kids.
I will say. You might want to get a color DMD for this one. And then it be a wash I think between which has the better display. Don't get me wrong Jpark has amazing animations. Love the T-rex chase, and the extra ball animation(one of my all time favorites), but with a color DMD the animations for the simpsons game basically look like the show. That is why I consider it to be a wash between the two.

Either way these are both great games. I'd rather own a simpsons. But, the pro for Jpark might be cheaper than a simpsons pinball party... One last aside... The pro might be less maintenance over the simpsons. But, you really got 2 great pins to choose from.

Don't doubt that. Just older games in general can be more work... But, then again some new games might be a lot of work too... Turns out I think I need to contact Stern and then take whole bunch of things apart on my brand new elvira... just to hit the ever important skill shot(don't know how that wasn't fully tested, before manufacturing. And that is why I actually hate. LE's being made first... Yeah, you're paying for a better package. But, the manufacturing process is still in its learning curve.

And some old games do turn out to be more reliable. Like my Sinbad. That thing is a tank as well.

So... I was just being more general about the situation. But, I guess... New or old. It's pinball. Crap is going to break, and you're going to need to tinker. That'ts the nature of the beast.