Similarly, 3) has the interesting assumption that you are not using BGP to talk to FooNet, which will not be the case if you have a multi-homed transit arrangement aside from the peering to BarNet.
No, I'm assuming you *must* have BGP sessions to everyone you get peering or transit from. The more places you peer with, the more BGP sessions you are going to have.
4) and 2) contain some interesting assumptions about meeting points and the topological relationships among FooNet, BarNet and the customer network. 4) seems to assume, for example, that more of BarNet's effort goes into a private connect to FooNet than to the public connect at BazNAP. Could be true; could be entirely the other way around.
That's not quite the assumption. It really is that more effort goes into a private connect to FooNet than to the public connect at BazNAP as it applies to your particular connection. They might monitor their BazNAP connection closely, but not be particularly concerned if they notice possible problems with a smaller peering connection -- especially if they don't charge for it.
As David's post points out, though, there is no easy assumption about what is going to be best. I think the Internet is actually best served by having lots of available of choices for how to interconnect. That way, when your mileage varies, there is something you can do about it.
Well, I won't argue with that. Another possible disadvantage with 'free' peering is you may have a harder time getting the larger companies to deal with issues that arise surrounding that peering. They may feel they have no financial incentive to worry about it, and you really have no contractual leverage to get, for example, response time guarantees. DS