I am reading through this thread and I see both sides just throwing stones at each other. This discussion will never work if both sides don't agree on some frame of reference. Anyways, here is my take on this:
T3 mex nerf (be it income decrease or price increase) won't have direct effect on early t3 Land because you are supposed to get t3 land BEFORE you get t3 mexes, that's what we are trying to achieve here after all, so there is no need to worry about balance of t1, t2.
What such change WILL impact:
For 1vs1.
Increase the importance and length of early - mid t3 stage (harder to transition towards more eco) which would be problematic if you don't adjust reclaim since it will deepen the issue of importance of reclaim during t3 stage.
Slow the game down after early t3 stage
For team games:
Force people to actually make some units during t2 stage or rush t3 to defend vs t2 armies (Before making t3 mexes)
Make reclaim more important past t3 stage and slow the game down (people will need to make some units leading to a stand offs with slow eco'ing (bcs of bad map design))
It's nearly impossible to change the game so that Team games become dynamic, the map design promotes more passive and turtly gameplay, and people play those games meaning they want such gameplay. I think that making a slight adjustment to slow the t3 eco switch a little bit would be good and healthy if properly implemented but you can't change the fact that still most team games will be passive and turtly.