I ended up filing a small groove into the mag catch. It is pretty small, but it provides significantly better grip with my thumb when pushing it back. I have not found it to present any snagging risks on trips in and out of my pocket.
Yes, I fully agree about carrying another mag. Regardless of what gun I carry, I always carry a spare mag. Having been to a few tactical and defensive pistol courses, it is amazing how fast you can burn through a mag in a high-stress situation. One course had us shooting at cardboard silhouettes starting with drawing, pointing, and firing double tap shots. At one point the instructor made us stop and guess how many shots we fired and how many were left in our gun. None of us guessed correctly, but all of us thought we had more ammo in our guns than we really did. One thing the instructor had mentioned was that one must always keep in mind the status of your weapon and to maintain readiness even after the threat appears to have subsided. That could mean reloading your gun with a fresh mag even if you still have a few rounds left.
The example above is in no way a "high-stress" situation compared to having bullets or a knife directed at you, but when we did some head-to-head shooting on steel plates, my adrenaline was flowing and I know I was not thinking as clearly as I normally do when just leisurely punching paper on my own.
I completely agree that the R9 is not the pistol for any significant engagements, but nobody can predict when bad things will happen and what the outcome will be. If it is the only gun you have one you when needed, then that is what you must use. Often times, it is the only gun I have on me depending on my attire for the occasion. I have never complained about having too much ammo except when it is in my range bag and the thing weighs a ton.