I'm not being funny and I hope you don't take offence, but you seem like a knowledgeable guy, make some your own parts, but you seem to be band aiding your bike.
You have rear tyre issues and make it sound like the ZX10R has some inherent problem.
Why spend time and avoid the enjoyment you could be having with your bike.
You do know that upon release, the gen 4 ZX10R was the superstock bike and pretty much still is.
The British Superstock championship was like a one make series.
This points to the fact that the bike is great as a package (especially for those budget restricted) but like anything, it has it's limitations.
Unfortunately that means sometimes spending money on the areas where the package is weak, but more importantly, getting the package set up by those of superior knowledge in bike set up.
Anyone can chuck thousands in Ohlins on a bike, but its those with the knowledge of set up that can make it work.
So start with the basics...Is the suspension in good condition? Anything that came in the bike fluid wise is trash. Even more so if never changed.
If the stock suspension is good, has a professional set it up for you in terms of your riding style and weight?
Those suspension people at the track have limited time and unfortunately sometimes knowledge. I once had a track suspension guy tell me my rear Ohlins on my K5 was shot only for me to take it to Steve Jordan and him show me it was completely fine. I know who I'd trust.
Your reasonably quick so you are now reaching the limitations of a bike designed to work on the street and sold for a budget.
Its a good package but even I'm finding its limits just riding on the street compared to my Ohlins K5.
This is not an ode to the ZX10R and yes there are better bikes out there. I think that BMW will definitely have strengths over our bike and the new R1 when set up could probably run rings around it with a semi good rider onboard.
But...You haven't seen your bike in the best light, so I don't think you're making an informed decision.
Ofcourse if you just fancy something new then I'll shut the fuck up and wish you the best, but for my money...
I'd give MCT Technics in Suffolk a call. Tell them what problems you're having.
Take the bike in with a budget in mind and have them work within that, whether that means a KTech or Ohlins shock and forks / cartridges or just them taking that crap shock off, taking it apart and fitting it with non crappy parts and non leaking seals.
Ok I will shut up now and good luck with whichever way you go.