I would say it depends on the project. Many people are using the full potential of the performance goodies they add to their cars by going to the track and really thrashing their machines. I can see where that percentage has little need for hi-powered stereos or heavily modified interiors. There is definitely a weight advantage.
On the other hand, the majority of projects, realistically won't be seeing a lot of track time. They are more than likely going to be street cars. Weight savings really isn't that crucial. However, the first thing people think about is usually the drivetrain,suspension then exterior and interior sort of brings up the rear. It's almost like an afterthought for many people. Granted, there are a lot of people who really like the look and feel of the classic or stock interior.
Personally, I think the interior and creature comforts are of equal importance since you spend so much time behind the wheel (especially on long road trips) while everyone else gawking at your paint or drivetrain.
Just my $.02