Providing these smaller rural Brigades with different resources is a good solution in my opinion.
I can't see the point in closing a Brigade with keen, active members.
Sure, a rural Brigade with 10 or so calls a year may not seem important but any rural fires in their current area will surely have the potential to be larger when waiting for resources from over 30km away. I also think it will place greater strain on the remaining Brigades to deliver services when they are likely already stretched.
As discussed in another post if you can only get 2 or 3 members out of these smaller Brigades it can really help to augment the "bigger" Brigade numbers particularly during "day" (work) hours.
I'd hate to see any Brigade around us go and would like to think that even if they felt that they were struggling that they'd receive support and assistance to stay rather than have the bureaucrats rub their hands together in glee
But I've always been a bit naiive.