There's a point where your focus of RC develops. I mod everything in every scale to get better performance but I feel confident doing so...
projects atm:
1/24 scale version of an AE B44
1/18th stadium truck out of Mini-T parts
1/10th scale high speed/high downforce 4WD car out of a Tamiya F201
modifying parts on both a AE TC4 and an XRay T2-007 to create different more easily adjustable camber/caster angles
I'm also learning to airbrush lexan
If you dont have the nerve to fool with your larger scale cars then tear down old xmods and build them into something new again.