... i agree with most of your views on the 4 models. Just don't agree with your conclusion, on getting the 4 of them is the difficult approach. I think its the easiest solution, you just need the money... The hard approach is having to choose ( And the headach that goes with it ) the one that we love the most now, and especially the one we'll keep on loving over time.
I own the 5070R, and even if i still love it (i'm a Rose gold fan), i find the platinum to be THE one. The power of the blue dial in combo with platinum is so strong, subtle, and screams Patek... in 1 word : SEXY!
1 point that you didn't talk about in your post, something IMO that is part of the DNA of the 5070, it's the rail of the chrono. Magical on the Yellow gold and platinum, its colored in a way that gives an extra boost to the dial. Especially the white rail on the blue dial of the platinum that pops out in a unique way. Wg and Rg, the magic is less obvious
The Wg is for white metal fans, but as you said, if its the most homogenous, it goes with anything you wear or any strap you put on, easiest to wear, the most readable one... But the drawback is that it feels a little "neutral" compared to the other 3. White metal tend to be cold, but i feel the Wg to be a bit "dry", lacks the waow effect, especially once you've seen the Platinum, which is the sexiest IMO. But a safe buy and THE all rounder.
As for my Rg, i love it... but just during day time and in sunny days. At night, it feels different, much darker and less readable. Unless i find a 5070P, i'll just wear it in the days 
And since i've toyed with the new chrono, i'm starting to feel that the Lemania took a beating
... a serious one. Let's wait for the new metal of the 5170 hopefully next year, otherwise, we'll have to collect the 5270 line, and that's gonna hurt even more!! 
Thanks for the great post