my understanding of the energy absorbing mounts is that this was a requirement by ARB to satisfy the Australian equivalent of DOT as it relates to airbag deployment. by absorbing impact energy (similar to a stock bumper) this preserves the factory intended deployment timing of the airbags, where an impact without said zones could result in premature deployment of the airbags. (one of the main reasons i chose ARB)
So a solid mounted bumper (all others) may be stronger and take a harder hit, but would not avoid or eliminate the deployment of airbags, if anything it would cause that to happen sooner than if you were stock.
its been years since i researched all this so take it with a grain of salt, your mileage may vary, yada yada yada.
regarding the frame modification, my take is this. It is advisable to do it, BUT if you do not plan to do any winching i think you'd be fine without it. I as well as a few others i know ran for years without the endcaps with no ill effects. that said, none of us were ever doing any winching.
I had read some time back on a tacoma forum that virtually all tacos who were doing any kind of regular or heavy winching were seeing deformation in the stock endcaps that the tacomas have. To install the ARB on a 4runner you have to cut the factory endcaps off for fitment so its actually a less solid install relative to a tacoma since you do not have that long bolt going horizontally into the end of the frame.
As for the mod itself, its pretty simple, it involves cutting a piece of angle to size, cutting a hole in it, tacking a nut to the back side and welding it in place. Several yrs after initially installing my ARB, I was lucky enough to have a friend do the welding for me. I wanna say that fabing the caps and welding them up took about an hour, maybe 2 tops.
If you are looking to pay a shop for the mod, i would count on removing and reinstalling the bumper yourself (or with the help of friend if you are installing a winch) Id prol wanna pick up the angle, nuts and bolts myself as well to ensure proper grading (grade 8/10.2) and so you are paying for labor only.
While the ARB does look a little bit dated to some, I love the way it looks and i have been very happy with it. It has saved me from some pretty serious front end damage on several occasion, and if i had to do it all over again, i may very well go with the ARB again.
Its been years since Ive researched this so ymmv, also i recall finding a lot more info about this on the tacoma forums.
here is a pic of my completed endcap mod
Good luck!
Edit: I googled tacoma endcap deformation and found this pic. As i recall, the "endcap" mod was actually invented (by necessity) on the tacoma side and eventually migrated over to 4runners for obvious reasons. Here is a great writeup on the mod:
http://www.nwtoys.com/content/123-frame-endcap-modification.html
