Shinichi Kudo is actually very well-rounded and has good look to boost, so he will certainly go places if he weren't caught up in that life-changing event.
On the other hand, Kindaichi has the brain of Shinichi and the personality of Kogoro. Kogoro can enjoy the bliss of being ignorant, but Kindaichi can't. His involvement in many cases has inadvertently put Miyuki in danger more than once. Even his kohai got killed. And many times he had to push his good friends to the corner and expose them as the culprits. It's inevitable that he will want to quit crime solving at some point.
And in case he wants to open a detective agency, he would need someone with the organization skills of Marin. There's more to making a living as a private detective than simply having a super brain. I still think being a salaryman is the best route for him. At least he won't have to think about where the money comes from each month. But the saddest part for me is that there is no reward for solving crimes at his age. A teenager solving crimes will be applauded, but a 37-year-old jaded man doing that is just considered as a troublemaker, or a busybody.