Although they can't require that you go to the dealer for maintenance, the burden is still on you to prove maintenance was done.

I am not sure that is true.  The burden is first on them to prove that lack of a particular maintenance could [reasonably] be the cause of the particular problem (at least, that is my understanding).   If it could be, then you do have to somehow show some type of proof.

Not having proper valve clearances, for example, causes very particular issues.

This doesn't mean the dealer couldn't just reject you outright, or even mama Kawasaki reject your claim.  It is more of a "if it ends up in court" situation.  One hopes it never would need to get that far. 

As far as the valve deal.... the odds are extremely low on a C14 that not having it done at 15K or 25K or even 50K would cause any damage because them getting out of whack enough to cause damage appears to be very, very rare.  This is a testament to the good design they used, and there are tons of posts here over the years showing the valves typically still being in the tolerance zone for way  more than double or triple the recommend USA check/adjust interval.

[...]Having that information will look a lot better than saying "well, I did it myself, and no I don't have any proof, but I swear I did it properly".

Very true... good record keeping is good.

  This is a testament to the good design they used, and there are tons of posts here over the years showing the valves typically still being in the tolerance zone for way  more than double or triple the recommend USA check/adjust interval.

Very true... good record keeping is good.

 
AND there are even more posts that were made by folks that actually trusted that a dealership really checked them..... I have seen very few of those folks post a shim map showing the actual measurements they encountered....

 Should I keep this bike for the long term what I will do is 1'st find a tech that I can trust to check all the valves at 20K-30K and pay to have all of them set to their max clearance. This would likely be expensive but more than likely be the last valve adjustment needed. At the same time having vacuum lines run to all the throttle body ports would make future adjustments painless.
 Max clearance could affect the HP slightly at upper RPM limits at the benefit of increasing performance at the low end. 

Should I keep this bike for the long term what I will do is 1'st find a tech that I can trust to check all the valves at 20K-30K and pay to have all of them set to their max clearance. This would likely be expensive but more than likely be the last valve adjustment needed. At the same time having vacuum lines run to all the throttle body ports would make future adjustments painless.
 Max clearance could affect the HP slightly at upper RPM limits at the benefit of increasing performance at the low end.

Personally I would never set valves at their max clearance unless they were easy to access so I could check them quickly and cheaply myself. Since it is a chore to access them to do the check, I would prefer to have them set near the middle of the acceptable range if I were to make adjustments so if they change adjustment at all they won't go out of spec so easily.

Personally I would never set valves at their max clearance unless they were easy to access so I could check them quickly and cheaply myself. Since it is a chore to access them to do the check, I would prefer to have them set near the middle of the acceptable range if I were to make adjustments so if they change adjustment at all they won't go out of spec so easily.

Well, they aren't easy to access to quickly and chaeply check them, with that said why would anyone want to set them anywhere less than the upper limit?
They will never move past that limit, they can only go the other direction....
the reason there IS an upper limit is because you can never make them exactly in the middle....
careful swapping of the buckets and shims during the process CAN make a big difference, and once set at the upper limits you really can stretch the interval safely.... just how far is a toss up, but easily double that when they are set mid spec.

jmho, having made these adjustments.....

Well, they aren't easy to access to quickly and chaeply check them, with that said why would anyone want to set them anywhere less than the upper limit?
They will never move past that limit, they can only go the other direction....
the reason there IS an upper limit is because you can never make them exactly in the middle....
careful swapping of the buckets and shims during the process CAN make a big difference, and once set at the upper limits you really can stretch the interval safely.... just how far is a toss up, but easily double that when they are set mid spec.

jmho, having made these adjustments.....

I see your point, but I have never set any of my bikes at the upper limit, preferring to remain somewhere in the middle. I might err on the high side but haven't set them at the limit. That's just me I guess. Shim and bucket valve don't generally move much after the initial valve check in my experience anyway, they can of course but they are fairly stable after the first check.