I still find it hard to believe that any team would be sandbagging in order to deceive other teams of their true pace. I think at this point, to the extent that teams aren't showing their full speed it is because they don't care and it is meaningless anyway. None of them know what the other teams are capable of at this point, so they are just trying to make their own car go as fast as possible. When race day comes, we will see who was most successful at that.
Just think about why a team would sandbag; they don't want other teams to know how fast they really are, so that... what, the others don't steal some innovation they have? As if other teams aren't already looking for innovations everywhere they can? I mean what, Ferrari is going to ignore the Sauber unless it runs a really fast lap, and then they are going to send some spies out to investigate? I think all the teams are investigating all the other teams anyway. Let's face it, a slow team may come up with a good innovation and just not be able to exploit it.
Next, there is no reason for Red Bull to sandbag because everybody expects them to be fast anyway. Same for Ferrari. Same for McLaren. Every other team will already be looking as closely as possible at those teams because they have the resources for the research and innovation. You could make the case that Mercedes or Sauber or Williams or TR or Lotus might not want to show their true speed, but the fact is, those are the guys that ARE showing speed, so they don't seem too concerned with tipping their hand. The rest of the teams would LOVE to have a run at the top of the timesheet don't you think? What a morale booster for Catherham that would be!
There is also a difference between a visible innovation and a hidden one. If a team has some internal magic going on, the other teams aren't going to be able to see it anyway, so no reason to sandbag it. So it would only be a visible innovation that would be subject to a sandbagging strategy, but because of all these other reasons, that seems unlikely too.
Finally, if a team has some top secret innovation, they are going to want to try it out as soon as possible. By it's very nature of being unique and creative, it will have a large "unknown" factor and need some testing time.
My one caveat is that a team may discover something during the course of testing and end up bolting on some magic parts at the last minute that might make it LOOK like they were sandbagging, when in fact I think it is much more likely that they really got the parts on the car as fast as they could.
That's my 2 cents anyway.