I think it depends on the person and the relationship. Some people will allow themselves to get lazy and will stop trying/get complacent. Some will be happy to use their experience to keep having hot exciting sex and will be confident enough to want to try new things and work at it.
And depending on physical health, that can affect it a lot in terms of fatigue and stuff too. I know at a certain point my bf got so busy with his last year of college and multiple jobs that he truly didn't have the luxury of being able to keep up with his fitness or his diet. He was so busy he was lucky if he got 2-3 hours of sleep a night. It really fucked with his health so he was always tired and achy and getting sick. Our sex then was still good, and a lot more adventurous than some people's, at least, but it was definitely a lot tamer than it would have been otherwise. We're usually the sort that fucks in every direction and upside down. It's better now though.