Just read through the whole thread. After seeing all the pics shared regarding inner tire wear it's very easy to see that this is a toe problem, not a camber issue; the pic OP posted makes it definitive. If this were camber related at least 1/4 of the inside tire would show uneven wear compared to the outside tire. Since the excessive wear is focused only on the inside shoulder though, this is 100% an issue caused by lack of sufficient toe-in.
Contrary to popular belief, ~1.8* of camber isn't all that excessive; certainly not excessive enough to cause any appreciable amount of wear on the inside edge of a tire (not on it's own, at least). My last 3 vehicles ran -2* of camber and went 60k+ miles on the same set of tires with zero issues. The only time I had an issue with inside tire wear was when, you guessed it, there wasn't enough toe-in being accounted for. In that case, going from 1/32" toe-in to 3/32" toe-in completely solved the issue, even with the seemingly high amount camber specified.
For those that would feel better about having less negative camber in the rear though, go for it; all that's needed is an adjustment to the cam bolt located inboard on the lower control arm. Yes, the service bulletin will tell you that bolt is only meant to adjust toe; that isn't entirely true though. To avoid another 4th gen RAV4 adjustable toe arm fiasco, in Toyota's infinite wisdom, they decided to do away with toe-specific adjustment altogether on the 5th gen. Now all you're left with is direct control over camber instead.
As we all know though, when you adjust camber, toe values also change, which is why you always adjust camber before you begin setting toe. So now if you want to adjust toe in the rear using only factory pieces, you first play with the camber cam bolts until toe is where you want it...then cross your fingers and hope that you end up with camber figures that are fairly close from side to side after the fact. Any mechanic, technician, or service writer that tells you anything different from the above is either lazy, inept, or both...but given the single point of adjustment meant to correct two entirely different variables, I can kind of understand why they usually don't even bother attempting to adjust anything in the rear to begin with.
To sum up, here's the most effective/efficient way to solve the issue of inside tire wear on rear tires:
1. Adjust camber to whatever you feel most comfortable using the factory cam bolts. They have a massive range of adjustment, so they are more than capable of hitting any value 'within spec' or otherwise. Although adjustable Cusco upper arms are high quality components, there is absolutely no reason to spend money on those when factory bolts will easily get the job done here.
2. Replace the toe arms with the Hardrace versions mentioned above. These seem to be the only adjustable toe arms made for this platform that have a rubber bushing as opposed to spherical units. If anyone else happens to find another solution here, please share.
3. Now that you have complete independent control over toe, without the side effect of adversely affecting camber, add as much toe-in as necessary to offset your respective amount of inner tire wear; I'd start with the most conservative value mentioned as Toyota specification (0.10*) and go from there, knowing full well that additional toe-in beyond that spec may be required to get the job done...and I suspect it will. By my calculations, the above figure should translate to 3/64" (per wheel). Adjusting for overall load, bushing deflection, etc. you will likely need more than what Toyota typically calls for in order to achieve completely even tire wear.
4. Profit.
