The quickest and easiest way of telling whether or not it needs to be done is by two methods.

First, clean the bore real well, including the crown. Fire 4-6 shots, and look at the powder residue on the end of the muzzle. If it is not extremely uniform, so much so that you can't tell that gas is escaping more from one side to the other, it may be okay.

The second method is, if it's a factory rifle, more often than not, it will benefit, or if it shows signs of wear like you mentioned earlier.

Nine times out of ten most barrels can benefit from a recrowning that is done properly, and yes it will greatly determine the accuracy potential of the rifle. It's one of the easiest things to correct, and it seems to be overlooked more than any other problem.

Well, here's a chuckle for ya'll. Went to the range this afternoon and fired 3 fouling shots on a super clean barrel (Walmart SuperX 270 Win 130gr Silvertips), grouped .4" center to center. Then a 4 shot, five shot, and another 5 shot group cleaning between groups. 1.25" to 1.5" between the three, using Scott's (that would be me)in-famous handloads...while the crown may not be the sharpest around, it looks like I need to hang around the reloading forum a little more often!

Funny thing, but there are still a lot of guys (gunsmiths) out there that simply run the barrel in a steady rest and cut the crown without any consideration given to the concentricity of the bore.