Just playing Devil's Advocate here - if you're only going to make slight mods as you've said above, then you're really not likely to see any noticeable improvements in either fuel economy or performance.I'm not really gutting the interior, just took the back seats out. And taking little things out here and there, but its still going to look like a stock STI when you look inside, for the most part of since there are slight mods being done
Without any noticeable improvements in fuel economy or performance, I guess I don't see the benefits of what you're proposing. Of course it's your car and you can do what you want to it. But it doesn't seem like a project that has a rational explanation.
Just my two cents.