1. Rasho is the best defensive center we have, since Tim plays PF.
2. Pop will play Rasho heavily against Detroit, Miami, and Sacramento. Against teams like Phoenix, Nazr will be played because of his more reliable offense. Dallas could go either way, depending on how they play.
3. See above. Rasho is EASILY the better fit against defensive-minded teams. Nazr brings more defensively, and is a good rebounder, but against quicker teams he tends to bobble the ball.
4. That depends on who the Spurs play.
5. I disagree. Pop and the Spurs LIKE Rasho, and Nazr will likely be overpaid this summer, if you look at the going rate for mediocre centers last year. Nazr will not return if wants a big contract. It would be a mistake to let Rasho go in favor of Nazr; Nazr is more replaceable.
I think the initial post in this thread provided excellent analysis of why Rasho needs 15+ minutes for the Spurs to win. It doesn't matter as much who starts, as it does utilizing Rasho well.