This is probably a worst-case scenario. What about Ethernet cross-connects using the 6 port cards? Or zero-mile T1's using the 8 port serial cards?
I keep thinking that I live in a world where providers have MUCH faster trunking pipes than the pipes they sell to their average customers. If you can get away with a T1's worth of bandwidth, then the only reason you and your "peer" would be in the same room is to share access to longhaul, and failing that cause, the situation you describe would not occur and you would just run the T1 through the TelCo from your closest hub to theirs. Ethernet is a slightly different case but only slightly. An ethernet switch costs a lot less than a GIGAswitch, or for that matter, there are probably occasions (as occured at the Phoenix IXP) where unswitched 10Mb/s Ethernet is a fine way to start out -- which means you can grow to a switch and even to 100Mb/s if you plan it right, but you cannot easily grow to FDDI (which some customers think you should have to get them 4K PMTU to their semi-local destinations.)
And you are assuming a full mesh which isn't necessarily what people need.
I thought I'd covered this. I'm assuming full mesh because if you are paying to colocate equipment and tie your colo back to the rest of your net in some way, you will pretty naturally want to get as much bang for your buck as can be had. Each person you don't peer with represents additional load on the people you do peer with, or on your upstream transit if you're buying any, and on the upstream transit link of your unchosen-peer if he's got transit. Once you're in the same room, the cost of not peering is a LOT higher than the cost of peering, unless and only unless you already have a private interconnect to the unchosen peer.
I don't think you can generalize about what a provider wants from an Exchange Point especially not in a world in which exchange points are breeding like rabbits.
I agree that we're going to see a lot of IXP's of all sizes and shapes soon.