Your question could deserve a book-length treatment, but one quick thing I can say is that the system is self-correcting. The more bells and whistles you add on

Your question could deserve a book-length treatment, but one quick thing I can say is that the system is self-correcting. The more bells and whistles you add onto the Standard Model, the less anybody else will want to build upon it. And complexity doesn't rise steadily over time. Because of the LHC results, many models these days are a lot simpler (at least to me) than 10 years ago. It is true that in addition to bolting on correct features, you occasionally need syntheses that simplify the whole thing, like how the zoo of mesons and baryons were explained by quarks. But at the moment, we're very far from having that problem...