Would it do anything to change the films? No? okay......

Godzilla's size changes for reason's other than just plot/asthetic reasons. Godzilla  maintains a height consistant with the era he is in. What this means is, Godzilla from 1954 being only 50 meters tall, would be dwarfed by modern architecture, and would make him way less imposing. Upping the size thoughout his filmography was done in an attempt to keep him relevent as technology progressed and buldings and skylines grew.

oh thanks petedjog :)

Actually the big change in size was more of a financial reason for Toho, they cut back on the budget in the 90s and made him 100 meters to make the minatures smaller and save money, the fx crew hated it because they couldn't add as much detail to the smaller models and thought they looked faker.

As far as destruction goes it would really depend on personality. By the time the 70s came around and Godzilla was a hero he'd practically walk around a city to avoid accidentally knocking over a building