Why has no one answered this?
Basic answer is yes, there are advantages to doing most adjustments in ACR instead of waiting until you get the image into Photoshop. Most, but not all, in my experience.
Doing tonal adjustments is better in ACR, especially in the new ACR 7 with the "2012" process with its highlights and shadows features. It's easy to test this. Take one of your images and fix the sky in ACR. Then pass another version to Photoshop without the ACR fix and try to do the same adjustment using Photoshop only tools. Be sure to pass the unfixed version to Photoshop in the ProPhoto colorspace to make it a fair contest.
Repeat with some midtones or shadows. If the adjustments are conservative you might not see much difference. But when the adjustments get more aggressive, the advantages of ACR will show up. For example, take a badly underexposed image and do a +1.5 exposure adjustment in ACR and then try that in Photoshop.
On the other hand, I find saturation (and vibrance) adjustments are better in Photoshop than in ACR. Primarily because in Photoshop you have access to more advanced saturation adjustment tools (Channel Mixer, LAB mode) and sophisticated saturation masks. But also because if you push the ACR Saturation slider to extremes, strange things can happen. Out of gamut colors are reached much sooner than with the basic Hue/Sat slider in Photoshop.
Sharpening and noise reduction is still highly debated. Some argue that ACR is better, some argue that Photoshop is better. Again, those arguments sometimes hinge on the ability to use advanced masking in Photoshop.
Which brings up your other question of the Adjustment Brush in ACR. Personally, I find it to be a crude and difficult tool to use. But that's because I've spent years masking in Photoshop, either by hand with paint brushes, or with other semi-automated techniques. I'm real comfortable with Photoshop "brush masking". Can't get comfortable with the Adjustment Brush in ACR.
Bottom line, I think your technique of making 2 or more ACR versions of an image and masking them together in Photoshop is a a good one. A lot of famous gurus advocate that approach. You get the best tonality from ACR and the best masking from Photoshop.