I wonder if the apparent freedom in VK had to do w/ the Coppola connection
Never considered that, not sure if Coppola's "pull" had any effect on Cage's early roles, aside from maybe helping him land them in the first place. Though presumably, part of the reason Cage changed his name was to try to downplay his connection to Coppola. Of course, the other reason was because he's apparently a huge comic book geek and wanted to name himself after Nick Cage from Marvel comics. He even named his kid Kal-El after mother####ing Superman- that's some next level comic book geekery.
Only films I've seen out of the ones you mentioned are "Fast Times" (good but agreed that it doesn't count) and "Wild At Heart" (yep it's crazy but the craziness obviously has more to do w/ Lynch than Cage). I guess "Deadfall" is another film w/ a notoriously crazy Cage performance but that one didn't come out until '93. The clips below make it seem like he may have been drunk/on drugs the whole time but maybe he's just playing it that way. HI-####IN-YA!