Speaking as a "new person" (more or less) -- the porch swing thread *does* intimidate me. Too many pages, too many postings...it's hard to jump in at the end not knowing the preceding conversation, and there's too many pages of preceding conversation to try and catch up.
That said, I just looked and the current porch swing has 12 pages and 231 replies as of 45 seconds ago. It's hard for me to suggest a good point for starting a new one... maybe 5-6 pages? 100 replies? My greyhound message board (I don't own it, I just live there) starts a new thread at 50 pages, 1000 replies, so I feel like a wimp saying 12/231 seems like a lot. But I never go in the greyhound chat thread either.
Maybe I'm just not a chatty cathy (my friends would NEVER buy that).
(Totally off-topic in my own post -- I just found out I can drag and drop text. I highlighted something to delete it and dragged it instead. It moved, and stayed moved. COOL!)
You might consider starting a new porch swing at 6pages a few times, and see if that increases participation. If it doesn't, then go back to whatever you're currently doing.