Hiya,
I think its a great idea. I still 'hang out' in the SMEP buddy group cause I love the gals there (even though I shouldn't be there as we have been diagnosed with MFI and have been undergoing IVF for the last 6 months).
The problem is, that most of the original group have graduated, but there are still a few of us 'long timers' in there. While new members are always welcome (so please come and join us), however as the SMEP seems to have quite a good success rate, often new members get a BFP on their first month. This is hard for the original members. (I'm one of them, so feel qualified to be able to say this)
I'm sure we are not the first buddy group to have this issue!!
However, I guess the same thing would happen if you started a 'long term' TTC buddy group though, as (hopefully) members would get a BFP. So its not a sure way of fixing this problem. I don't want to offend anyone, but it is hard when someone gets a BFP in the first month or two or even three or trying, especially when you have been trying for several years!
The hard thing would be defining what a 'long time' is. I'm sure there is lots of different opinions out there. My friend who was trying for "ages" and "knows how hard and stressful TTC it is" was telling me that after she "relaxed" it happened. And maybe I should "relax" as well.

She fell pregnant in her third month of trying.
What I am trying to say is that time is relative. What seems like a long time for some people is noting in comparison to other people.
Anyway, after all that waffling, I guess I am trying to say that yes, its a great idea, and I would love to join!
Thanks