I have an eighth level cleric archer. Currently with weapon blanches, align weapon, blunt arrows, and holy weapon balm I am not sweating DR that much. I am still going to take clustered shots at 9th however simply to help deal with the fact that alignment based DR is getting more common and also DR slashing.
Basically DR/magic, DR/piercing, DR/bludgeoning, or DR/material are easy to get past and carry arrows for. It is alignment based DR, epic DR, or slashing DR I will take this for as while I get many attacks as an archer my damage is still only 1d8 + 14-16 depending on buffs so any non bypassable DR greater than 5 hurts a lot.
Hope this helps.
Just take the feat unless you feel you can't work it into your build for some reason.
Relying on spell slots to get through DR isn't going to be effective.
That said, durable arrows of materials work fine for a lot of stuff.
I know a lot of people love clustered shots, but I've never been too impressed with it. Arrows are already so versatile for overcoming DR compared to just about anything else.
I think that you can almost always do better with a different feat.
Assuming your character isn't a complete dullard and someone in the party can identify it, it's likely you would know what types of materials would bypass a creature's DR.
If you're asking a more general question of "Is it metagaming to know certain arrows can bypass DR of certain creatures but my character doesn't know that..." my response is, have you met a single creature with DR? Does you character know about cold iron and silver?
Yeah, its probably not metagaming at all to purchase arrows made of special materials to bypass DR. You're an adventure, this is like adventuring 101 information. At the worst case scenario, first time you encounter a creature with DR you probably realize the situation. So you buy a grab bag of all the arrow types you can to bypass DR, because you don't know what you will encounter and want to be prepared.
So I recommend going ahead and buying durable silver, durable cold iron, durable bludgeoning arrows. Durable adamantine arrows are expensive, probably too expensive to bother with.
My biggest problem was overcoming alignment based DR as an archer, without clustered shots. Although it was rare that it came up before I got the feat. Still, being able to mostly ignore alignment based and adamantine based DR before I had +4/+5 weapons was useful.
Even though you can get arrows to help with a lot of DR, I'm still a fan of Clustered Shots. Specifically for DR adamantine and alignment.