It's RC, not Formula 1, Moto GP, Supercross, or anything like that. Sure the top guys are getting some parts to test here and there, but it's their job.
The factories depend on these drivers feedback in order to develop the cars and give you and updated kit to buy. So yes, there will be some parts you see them testing that never go into production. If it doesn't reach production, it's because it wasn't suitable and you don't want it anyway. \
As far as motors and fuel, they will be running something you can't get there too from time to time. They aren't doing this for any sort of advantage or edge, it's for testing. I've talked to numerous pros running off the shelf motors.
I tend to look at testing prototype parts as a disadvantage sometimes. When dealing with a 1 off part, durability can be compromised. It may also have adverse handling effects that doesn't fit that driver. You never know. I say let them do what they are being paid to do. I'll keep running my mostly out of the box kit with the few tuning options that suit me best.
I've also tried some pros setups early on and struggled with them. I learned to find what works for me, not someone else. Granted, as my driving has progressed, my setups have drifted closer and closer to the pros.