Color space inaccuracy at the telecine conversion and the ability of the light sensor to pick up these or display deviations from the presumed or assumed NTSC or ATSC x-y Y coordinates would I'd have thought be beyond the scope of a thread on SpiderPro. If you know what you are doing you would not be using the SpiderPro with its software. You would already have someone's software suit and all of the other essential calibration tools. You might or might not use the Spider as a sensor, but I somehow I suspect you would not. I am more of a real world individual and I'll accept some of the presumptions in a piece of inexpensive test gear, like the Spider and live with the potential and likely inaccuracies. Where are you going to stop? CIS-200? CIS-2? CIS1? The SpiderPro is really a good value and it will get you part of the way to heaven. However, should you want to get the most bang out of your display you will need better tools, better software, possibly pods with more then a few sensor points, and some experience--which may, as you imply be the most important criteria of all. A tool is still a tool and requires a skilled user to get the most out of it. But the full suite is necessary if you want to perform a full calibration. At some point you have to live within the standard deviation of your tool or use your eye as a corrective. Personally, I depend more on my eye than the tool but your damned right I begin with the metric I obtain from the tool.
For the record I work for no company with a direct stake in the calibration game save my own so my opinion is not colored by a desire to see any single product from any manufacturer succeed or fail. I am not pushing product A over B nor suggesting anything other than the Spider and its software only permits basic calibration using front panel TV controls. This is a thread on Spider so my comments are directed towards the Spider. I am not suggesting that any particular software suite is superior or suggesting which tools to use. I am arguing that the Spider is good value and that at some point there is a diminishing return on investment. If you want more accuracy you will need to go past Spider's software towards some other, from whomever you might choose and certainly towards a pod with more sensors and accuracy, though I am uncertain if even the most expensive sensor would necessarily discover any and all deviations from the presumed color space co-ordinates. Ultimately, video calibration requires tools but, like audio, is as much art as science.