@Laverdalothar the one advantage that California has over Germany and other places is no TüV or MoT inspections for our bikes, and therefore unlimited modification without approval. No official technical inspection has ever been done on any of my motorcycles, ever, since new. So we scurry about making fake emissions compliance stickers to get the bike registered, but nobody cares at that point or forever if the only ‘correct’ thing on the bike is the sticker.
My wife is Bavarian so I’m roughly familiar with the comparison. Neither Germany or California is as good as e.g. Montana or Florida for lack of bureaucracy and reasonable costs, but unfortunately those latter places don’t have so many twisty Alpine roads!
I am not sure if having no regular inspection is an advantage really. Yes, it can be annoying, no doubt. However, the TÜV equivalent called DEKRA has found at least twice issues on my bikes I wasn't really aware of. Once it was the scooter of my son, which we wanted to upgrade from 25km/h to 45km/h speed limit (different driving licenses - don't ask...). I recognized that China banger was behaving weird (self turned to the right), but could not tell what it was. When the TÜV-guy jumped on it, it took him just 2-5 meters of driving to tell me that something's wrong with the stearing head or the fork.
At home, i found the lower triple clamp (well - it just has a lower one actually) was bent and the while wasn't straight. Did not really recognize that... Bought a used one for 25€, new bearings and all of a sudden, you could ride that thing freehanded!
Similar issue on the Vespa of my wife: it was actually running fine and straight, but turning was a bit of an issue sometimes. DEKRA guy controlled the headstock and found it was not freely turning. Returned home, took things apart and found the grease to have hardened. removed it, put in a new bearing (allthough the old one was still good, but I had it handy...) and voila - free turning headstock!
1000 SFC once was at OCT years ago. TÜV guy said, the rear wheel bearing wouldn't be OK anymore. Roger later tested it again and said that he can not find anything wrong. Told him I want to go to italy with the bike and he said that should be fine with no problems. 400km later, the rear wheel bearing was so damaged, the rear wheel started turning sidewards...
I understand the US point of view of being responsible yourself for the things you do. However, how many Motorbikers are really good mechanics? I have several ones and am not a good one either... Further to that, it's not only about protecting you: if you have an accident with the bike due to a technical failure, the bike can slide into other people and kill them.
Regarding tuning: I have done so many things to my bikes, all of them have TÜV-approval. Even the 3-1 Megaphone exhaust is still in the papers, it might be illeagal though (and defenitely not environment friendly or good for the relationship to my neighbours... ;-)
So - there is good and bad in both systems.