I can answer the ammo question.
The "is the Special Grade worth it" is harder to answer, as it depends on what you value. If you want a rifle with genuine "I've been in WWII" history, the Special Grade has less of that. If you want a "shooter", the Special Grade has a new barrel. If the new stock is fitted correctly, it should be more accurate than an older rifle with a worn barrel and sloppy stock fit.
Back to the ammo -
All Garands (including Springfield Armory 7xxxxxx clones) have the same op-rod assembly, with its inherent weakness. The pressure curve of the ammo is the problem, not the chamber pressure. If you use modern hunting ammo, it is very likely that you will eventually bend the op rod or damage the receiver heel due to the slower powders used to achieve modern .30-06 performance.
It isn't going to happen with one box, so there is quite a bit of "Aw, I shoot commercial brand Y .30-06 in my Garand and I have no problems" going around. Note "eventually" in paragraph above...
The solution is to swap out the GI gas plug (gas cylinder lock screw) for an adjustable one, such as the McCann or Schuster. This permits "tuning" the action to just cycle reliably with whatever commercial .30-06 you happen to want to shoot.
You have to do the gas plug adjustment procedure every time you swap loads, as the pressure adjustment is not automatic.