Who's Going to Buy the International Space Station?

It's interesting to read about such prospects, but quite a few questions here are left aside.

Why 3-4 billions upkeep a year? Good analysis would probably break this into smaller chunks, like transportation - crew and cargo, communications - some satellite links as well as ISS-Earth ones, ground control for systems - keep working existing ones, add and replace what's necessary, space defense - from meteoroids, management for utilization - who when uses what how... what else?

Is splitting the station better than making specialized - perhaps free-floating - units in addition to what's already there? In this sense current ISS serves as an extendable platform to future manufacturing, assembling, experimental, tourist, refueling and other modules, but the one which is already "flight proven", the core of infrastructure. ISS itself started similarly with core modules which ensured minimum of functions allowing it to grow from that.