If I'm understanding this accurately - being a Platinum Pass Holder will get you in early every day for the ERT so belonging to a club becomes a moot point for most KI enthusiasts (please correct me if I'm wrong).
I joined Coaster Buzz last year, mainly selfishly for Boo Buzz which gave us an ERT hour on Maverick (I got 9 rides within an hour - my daughter got 11), however it's an affordable club and the membership appears to work for things like this, Coastermania and benefits like at Holiday World.
I saw that Coaster Fanatics also has a club you can join.
Someone official will need to judge on what counts for KI or not.
Perhaps for some people, but actually it's not a moot point for me at least. Since I am touring many different places all over the US to ride coasters between this year and next year. (I wish I hadn't missed so many at Cedar Point...) At any rate, Kings Island is my home park and I enjoyed the coasters at Cedar Point as well. So I figured the Great Ohio Coaster Club was appropriate since I'm such a fan of KI.
And yes, I too want the ERT time for opening day. I don't care about the rest of the year... I won't be up early enough every time for it to make a difference.
However, it would be nice to meet some other people whom are into coasters. There isn't really a group in my area that I know of... so Ohio is the closest.