I was unclear on the tax point, sorry; the extending of the baseline may determine the entitlement to tax resource use and extraction. You are correct in that UNCLOS prohibits tax of innocent passage.
On shipping it is also my understanding that UNCLOS grants broad rights to passage, though these are subject to those exceptions you mentioned, as well as an exception for "internal waters". I believe a couple cases turned on islands (which I am sure you also know about better than I do– my background is academic and dated!).
As an interesting aside, the word tariff comes from Tarifa, Spain, which would tax ships passing through the Strait of Gibraltar.
Just for ease of any future readers, the actual convention is not horribly complex, and is at: http://www.un.org/depts/los/convention_agreements/texts/uncl...
There are a couple exceptions for things like drug smuggling and terrorists, and now there's some concern whether these rules (fairly vague on paper) will be exploited by some for extensive search & seizures.
I made a site explaining the South China Sea disputes in particular if anyone is interested. southchinasea.co