This just popped into my head: Earlier this year I watched a fairly minor 70s sci-fi flick called The Ultimate Warrior. Nothing special. I recommend it only if you're really into such things and even then it's probably ok at best. BUT the saving grace of it is that it's two leads are Max Von Sydow and Yul Brenner. Replace them and the movie is probably unwatchable, Von Sydow in particular. It's a fairly nothing part and it probably allowed him to buy a new car or something, but he takes it completely seriously and its that gravitas that gives the movie its most redeeming quality.
I saw a Tweet Monday from the writer Mark Harris (who's great and you should follow if you're on the platform and into movies). I'd embed it, but I suck at those things so I'll just summarize.
He said you could hold three different full and fulfilling film festivals built around Von Sydow:
1. Bergman Von Sydow
2. Paycheck Von Sydow
3. Miscellaneous Von Sydow
I don't know how many actors your could say that about.