I was at the Coventry Vs Pirates game (pirates have the best chant btw). It was close to full with a good atmosphere, but that was around 2500. I expect that the capacity of the bpa is around 3000.
From what I can gather neither the fans or the owner have any ambition for premiership rugby, it's just too expensive.
Pirates chant:"Give me a P (P), give me an I (I), give me a R (Arrrrrrrrr)!.