You're giving up too easily, Russell.
I don't think many people browsing an astronomy site would listen to podcasts (maybe because it might be an older audience). So it's a question that many would find difficult to answer without experiencing it.
If Mike had asked if people were interested in an astronomy site/forum when he first thought of it, he wouldn't have started. Trust me. I was there when he said it and I said "Nah...I don't know... who'd be interested in that."
What I'm saying is, don't get discouraged if you think it's a good idea. Sometimes you can see what other peole can't. Fill a niche market and you'll have an audience.