Beanie,
Your case bears striking parallels to my own case, in which I was photographed by a "safety camera van" in August 2006. The road had a 30mph limit, reduced from 40mph in Sept. 1999. Then, as in your case, the speed limit signs were badly obscured by foliage. There was no system of street lighting, even though the police evidence presented in court falsely claimed that there was.
Some councils/police forces are still misusing the 1984 RTRA legislation in cases involving roads which have been reduced from 40 to 30, and which do NOT have a system of street lighting. What section of the RTRA have the police used to charge you? This is very important. It is also worth knowing that for a system of street lighting to be recognised as such for the purpose of denoting a 30mph speed limit, there must be at least THREE such lamps at intervals not exceeding 200 yds. (The 183m metric equivalent is used in Scotland, but England and Wales still use yards)
On the advice of my solicitor, I sent photographs of EVERY speed limit sign along the 1.1 mile section of the 30mph limit to the police when returning the information requested in the NIP. The police response was to decline to comment to my photographs, and to announce their intention to "continue the prosecution".
As for what happened between then and my Court appearance, I'll discuss it with you privately. But I can tell you that I went to Court, pleaded not guilty, and won the case.
As for the police "not believing" your pictures or any other evidence, that will be decided by the magistrates or even the prosecutor. When I pointed out the error in the police evidence, which stated that street lighting was present even though there wasn't any, the prosecutor readily conceded this upon a cursory glance of my pictures, copies of which had been sent in by the police.
In my view, based upon my one appearance in a magistrates' court, if you present your case reasonably and honestly, there's no reason for them not to believe you. So your photograph of the obscured speed limit sign, and your claim that the sign on the opposite side of the road was obscured by oncoming traffic, may well be accepted. Be prepared for the chief magistrate to ask you direct questions while looking you in the eye on that one.
I don't agree with what some others have said on this board, that the Court will press for a conviction whatever your evidence. It's just that there's a right way and a wrong way of presenting it. I was fortunate in having hit all the right notes.
Check your PMs for my phone number and get in touch.