I think your analysis in operating under a fallacy.
The problem is not the "common-ness" of magic weapons, the problem is how easy it is to penetrate DR, or if you can't how impossible it is to be effective. In other words, if you have GMW then you dont even necessarily need magical weapons (although due to gold being part of the equation in character balance, you WILL have magical weapons) to beat DR. But, if your GMW spell is not enough to bypass DR AND your weapon doesnt have enough +s (probably because you got other mods, depending on GMW to beat DR for you, or because you just got the sure-striking mod) then you might as well run away because you will not be able to penetrate the DR. This is the problem with DR as it is now.
With the new DR, magic weapons (Im analyzing here) will not be any more or less common. However, they will not provide the ease to beat DR that they once did. Additionally, the spell GMW will not be an immediate DR beater, neither will "sure-striking". In addition to this "nerf", you will no longer have to run if your weapon isnt good enough (or in this case, if it isnt made of the right stuff) because DRs have been lowered across the board. You can still contribute at, albeit, reduced effectiveness. These are pretty tough blows to "the munchkin" or "the powergamer". Not that theres anything wrong with min/maxing, thats a different argument. The point is, it will be more sensible to carry a backup weapon. 1st level packages will probably include 2 melee weapons in addition to a ranged weapon. This is not a "bad" thing. At higher levels, yes the fighter may have more than just 1 backup weapon. Will you be punished for not having multiple backups? If you see it that way, or perhaps it will be a good experience so that in the future you WILL have a backup weapon (as Hyp pointed out).
Players and characters generally know that it takes fire or acid to kill a troll. Good players may try and work off the premise that they dont know, but by and large people just know, maybe they heard a children's tale about it (their character, not the player) or what-have-you but its common knowledge for most campaigns. It will be more or less the same with the low level DR. If you are playing in a low level campaign there will probably be hints as to what you are fighting and you will be able to comission an appropriate weapon. I just don't see what not to like except the golfbag approach some players may take.
Net Munchkinism: No more Sure Striking, No more GMW abuse, No more Invulnerable DR. Possible cheesiness due to fighter having 5+ weapons. I'll take the new DR any day.
All of these are true regardless of the rarity (or non-rarity) or price of said special materials.
As far as your analyzation vs speculation debate, I agree to a point. But something youre analyzing may well turn out to be speculation and something Im speculating may well come to pass. In that scenario, what difference did it make how we were arguing?
Technik
The problem is not the "common-ness" of magic weapons, the problem is how easy it is to penetrate DR, or if you can't how impossible it is to be effective. In other words, if you have GMW then you dont even necessarily need magical weapons (although due to gold being part of the equation in character balance, you WILL have magical weapons) to beat DR. But, if your GMW spell is not enough to bypass DR AND your weapon doesnt have enough +s (probably because you got other mods, depending on GMW to beat DR for you, or because you just got the sure-striking mod) then you might as well run away because you will not be able to penetrate the DR. This is the problem with DR as it is now.
With the new DR, magic weapons (Im analyzing here) will not be any more or less common. However, they will not provide the ease to beat DR that they once did. Additionally, the spell GMW will not be an immediate DR beater, neither will "sure-striking". In addition to this "nerf", you will no longer have to run if your weapon isnt good enough (or in this case, if it isnt made of the right stuff) because DRs have been lowered across the board. You can still contribute at, albeit, reduced effectiveness. These are pretty tough blows to "the munchkin" or "the powergamer". Not that theres anything wrong with min/maxing, thats a different argument. The point is, it will be more sensible to carry a backup weapon. 1st level packages will probably include 2 melee weapons in addition to a ranged weapon. This is not a "bad" thing. At higher levels, yes the fighter may have more than just 1 backup weapon. Will you be punished for not having multiple backups? If you see it that way, or perhaps it will be a good experience so that in the future you WILL have a backup weapon (as Hyp pointed out).
Players and characters generally know that it takes fire or acid to kill a troll. Good players may try and work off the premise that they dont know, but by and large people just know, maybe they heard a children's tale about it (their character, not the player) or what-have-you but its common knowledge for most campaigns. It will be more or less the same with the low level DR. If you are playing in a low level campaign there will probably be hints as to what you are fighting and you will be able to comission an appropriate weapon. I just don't see what not to like except the golfbag approach some players may take.
Net Munchkinism: No more Sure Striking, No more GMW abuse, No more Invulnerable DR. Possible cheesiness due to fighter having 5+ weapons. I'll take the new DR any day.
All of these are true regardless of the rarity (or non-rarity) or price of said special materials.
As far as your analyzation vs speculation debate, I agree to a point. But something youre analyzing may well turn out to be speculation and something Im speculating may well come to pass. In that scenario, what difference did it make how we were arguing?
Technik