Along with depending on the guild itself and what membership benefits it offers, it also depends very much on you and which (if any) of those benefits you feel you'd truly make use of.
I have belonged to the SOA and to a local writers' society. At first, it seemed like it was worth the price tag: I went to a few meetings, heard some fairly interesting talks from professionals in the business, and even had my agent contract assessed FOC via an SOA lawyer.
Did any of that really make a difference? No, not really.
My agent told me that no writer she had signed had ever had a contract assessed -- it was a standard agency contract (they were a big agency) -- and, if anything, it made me look like an amateur (I was :)). If you sign with an unknown agency who might have the potential to fleece you, then getting a contract reviewed could justify membership (if they provide that).
Eventually, being the type of person I am, I couldn't be bothered to attend the talks (not getting enough out of them to justify the time away from writing), had no time for reading all the articles in the magazines they sent out (most of which had already hit the headlines online), and didn't really make good use of the membership services because I was too busy doing the job of writing.
No... agents don't check for membership, or troll their databases for talent; it doesn't give you kudos. Agents are interested in two things only: do you have an idea they can sell; and have you written it really, really well?
So, it really comes down to the benefits they offer and whether you (as a writer in the hinterland who's no doubt as insular as the rest of us writers) will really make use of the things on that list.
p.s. one thing I will say in favour of the SOA, is they are fighting publishers for fairer contracts for writers. Now THAT could be worth the price of admission!