The trending in i1P i lame, they didn't put their heart in it. If you don't own it already, don't spend the money for that!
X-rite used to have long term trending of many display profiles, I think it was in i1Match. And it used the measurement data I believe, not all those old and useless profiles to do this. Could probably do this in ColorThink, that' tool is worth every penny.
In the long run, all you end up seeing is how inconsistent the display is and it aid somewhat in getting you to re-calibrate more often.