The way I figure accuracy on semi-autos, the more everything is the same for each shot, the better the accuracy.
So, putting the buttons inside the stock keeps the op-rod more or less riding straight back and forth in the stock. You're trying to make sure it ends up in exactly the same spot for every shot. I'm thinking this could make a pretty decent improvement in accuracy--and if it doesn't you've spent virtually nothing but some time.
Another thing that might help, would be to figure some way to make sure the stock maintains its position to the gas block. As it stands, there's a slip-fit that's pretty tight. With the op-rod banging around in the forend and the barrel flexing with each shot, the stock is probably shifting around a bit and varying the pressure it exerts on the gas block for each shot. I guess you could carefully cut the stock back until it doesn't make contact with the block but still looks ok, but you'd also have to bed the action carefully so that it's supported without help from the gas block/stock joint.
Probably one of the best mods you could make to a Mini would be to do put a semi-heavy barrel on it. One that's heavier profile (maybe fluted to keep the weight down) under the stock/handguard but that is normal profile out past the gas block. I'm kind of surprised that Ruger hasn't done it already.
The most important thing with bench shooting is making sure you aren't muscling the gun. You want it to be just sitting on the bags. You're not HOLDING it in position, you're just aligning it and then letting it sit there by itself while you pull the trigger. If the sights start to move at all, stop and figure out why. The only thing you need to do is position the gun, hold it so it doesn't fall during recoil, and then pulling the trigger.
Also, memorize the sight picture (for iron sights) and make sure it's exactly the same for each shot. If you're shooting a scope, push it a bit forward in the mounts so that you can just start to see a ring of black around the edge of the picture. Keep the picture centered in the ring of black and you'll never have parallax issues again.