The Colts really have no reason to go for 16-0. You can look at last year and see that even though the Colts had to play every game down the stretch to hold on to their wild card spot, they still lost in the first round. Although that game against San Diego gets a massive asterisk attached to it. The Colts were literally a late pass interference flag against the Jaguars early in the season away from being #1 in the AFC last year. I don't even need to mention the ultra Hebrew officiating that happened in overtime of that game. I don't think it counts against the concept of rest vs rust. The Colts got mega jewed by a laundry list of factors, and San Diego was promptly exposed and eliminated by a team the Colts beat on the road in their own stadium earlier that year.
2006 is my favorite example of why you shouldn't rest after clinching, because the Colts looked like they were on track to do what they're doing this year and then collapsed for about a solid month before finishing strong and dominating in the playoffs. The key to that postseason run was definitely getting Sanders and Clark back healthy to start the playoffs. It's this reason I think the team really needs to not tank the Jacksonville game following this week's game should they win and clinch. The game would essentially mean nothing for them other than going undefeated in their division, but they need to make sure that if Gonzalez does come back this year, he's not coming back in a game that means something. They did that with Marvin Harrison in 2007 and he essentially blew the game for them with a bad fumble.
After that they'd be 14-0 and probably should sit starters after that point. Strangely enough I think the Colts B team is still good enough to beat the Jets and Bills and would give Caldwell a pretty good opportunity to showcase his coaching ability without having Manning and his stud defense to fall back on.