Even with purely selfish reasons I rather not have the exhaust drone or noise. I bought Lexus for quiet interior and comfortable ride, part of getting older I guess. I really like to hear without hearing aid when I get to 60. I had louder exhaust and loud stereos when I was younger, been there, done that, realized it’s retarded and moved on.
Sadly with Toyota and in general most of the naturally aspirated engines, there isn’t much anyone can do to improve much. There really isn’t any real return for the investment, turbos are completely different stores. I’m gonna leave mine alone and enjoy the reliability.
Only way to improve MPG is.....not drive it. Get a Tesla for week days and enjoy the weekends in the GX with much less guilt.