That's a tricky question, because while I would pay, say, $5 per month for it, if every existing user had to pay $5 for it, the value would decrease significant

That's a tricky question, because while I would pay, say, $5 per month for it, if every existing user had to pay $5 for it, the value would decrease significantly as most people probably wouldn't pay that much and it'd decrease my reach. If I were to pay merely for added benefits over what I have now, it entirely depends on what they would be..