Bill
I think your approach has some merits as a measuring stick but more stufy on this is absolutely needed.
Given what I've experienced recently I think the cost per prefix is greatly undervalued. It is actually a capacity/step change model that almost equates to the same model used for core bandwidth upgrades but the core bandwidth upgrades and the cost to refresh those has made the cost per prefix a non issue for the most part.
Unfortunately thats changing especially in the access and distribution layers of the network. Where for the most part there are devices that can currently cope with the bandwidth demand but can't cope with the route table size demand. I suspect any AS older than 5 years has a ton of kit that can't take the entire routing table and is causing major headaches and requiring rehoming of BGP4 customers to newer kit for no additional revenues!
Delivering BGP solutions for end users is starting to get very expensive particularly for those networks with lots of smaller pops, I think some effort to look at how this might be be
Regards,
Neil