This is the intake manifold on my naturally aspirated 1.9L SOHC engine at 190k...
https://1drv.ms/i/s!AhsZJDCN8kMMgRgDWyK3LiNYlQtv
That's all PCV and EGR. Since it ran cold, the EGR was completely clogged with ash. EGR is no longer used in many engines today. Up there, the oil & ash didn't experience much heat. Therefore the oil could be easily wiped off the aluminum. Didn't bother anything though but since I had the intake off the (cracked) head anyway I went ahead and sprayed it out with carb-cleaner. Drove the engine another 127k (>327k total) before selling the car over structural rust. Still ran great. This was well before DI technology. The four intake plenum pipes as you can see, are lifted from the floor. The clean throttle plate had a warning engraved on it about not cleaning it, as it had a special non-stick coating that would be damaged by the chemicals. Since EGR was post throttle plate, there was really nothing to get it dirty anyway.
If the 1.6L were known to experience severe build-up and serious running/performance issues as a result of valve build-up, it would be a different matter. But it isn't. Even the mechanic in the U2ube video stated that these weren't known for severe running/performance issues. If you're running 10,500 mile change intervals, stopping and restarting 20 times a day, modified your engine, use crap quality bulk mineral oil, spend the majority of time in creep & stop traffic at 220Ā°F, run without a filter, fill with Uncle Jed's Drive & Go bio-gasoline, drive at equatorial temps, or etc, or etc... probably have some reason to look into it. We have folks at 70 and 80+ (which ain't much) who so far as I've read, haven't complained of running/performance issues.
In theory valve overlap (a.k.a. "scavenging") is responsible for a significant part of the build-up. Here's the face of the valve on that 190k engine. Compare the exhaust valves on cylinders 1/4, to cylinders 2/3. (2/3 were being washed with hot coolant)...
https://1drv.ms/i/s!AhsZJDCN8kMMgR-ix6MgMbXCcRLf
https://1drv.ms/i/s!AhsZJDCN8kMMgTZLWUQ0G1B1Z_aZ
...that little bit of crud, if it were on the top would mean diddly. If you're racing then this will be the lesser of many factors to worry about... such as tuning, tires, suspension and driver training.