I guess the short answer would be twice as much work. You want the long answer too.
It would not be a simple case of replacing a low poly switch with a high poly switch. Both switches would need to be fully modelled and then UV mapped. Simple enough for a single switch but imaging doing this for the pilots seat for example. Building an aircraft from scratch is already time consuming, I have so far been working for some 2 months and I can safely imagine another 6 or 7.
In theory I could build an aircraft with no exterior at all and use all those wasted polygons for more detail in the cockpit, which, let's face it, is where we all should fly from. Its a flight simulator not a fashion show. But, I think the user base might throw a few tantrums if I did. I used to build custom models for P3D hardware simulators which contained only parts of the aircraft that the pilot could see and a landing lights/taxi setup. In the case of the hardware Vulcan simulator, it was landing/taxi light and a refuel probe, everything else couldn't be seen.
Question to Master Kenobi. Why does everything in the cockpit look smaller than it should. For example, a 2 inch gauge looks more like a 1.25 inch gauge.