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Air gauging is a method to check for variances in the bore size - the more consistant the bore is the more accurate the barrel should be.  It's often used to test match (or match quality) barrels.  If you're looking for a precision shooting rig it's probably a good idea, if you just want a plinker it's not needed.

Is Higher Pressure Testing w/ Magnetic Particle Inspection worth it?  The proof testing and scan can find problems before they are a real problem.  But honestly such issues are rare.  However usually companies that go through the process use the best of materials & QC so you can be assured of a good barrel.  Good materials, proper chrome lining, PROPER 5.56 chamber, and the barrel should be reasonably accurate.

Shops that don't follow those tests generally don't use as good materials (the old 4140 vs 4150 debate) but the real issue is what other steps are they skiping or skimping on?  Do their bores have more vairance?  Are their chambers truely 5.56? Is the gas port drilled right?  Front sight or gas block is pined in place with taper pins?  How often are they replacing their reamers?  

Remember the barrel is the heart of the weapon, if you really want a good reliable AR you want a GOOD barrel.

Now the cheap guys CAN put out a decent barrel, but they don't have the consistancy of the more expensive manufacturers.  Meaning you are more likely to end up with a barrel that lacks chrome lining (chrome-moly is NOT the same thing), or the gas port is slightly off in size making the rifle finicky about ammo, or the chamer isn't sized right/has machining marks so reliablity suffers untill the issues are addressed.

If you just want a plinker yeah you can get by with a cheap barrel in most cases - if you do get a bad one we have a really good troubleshooting section here on AR15.com to help you get it running right.  If you want something truely reliable and dependable I'd spend the money on a really good barrel.

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...however when the barrels are from the same company would it still be any real concern?

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Woa what do you mean 'from the same company'?

Are they manufactured by the same company?  

And if they are - are they from the same batch?

AFAIK Palmetto doesn't manufacture their own barrels - so they are outsourced.

Lots of variables, and you can't make assumptions about one barrel type because the retail also offers an upgraded model.  Are they safe?  Yeah I'd bet they are.  Are the non-air gauged ones as accurate as the gauged ones?  Maybe, it's possible you get a good one, it's possible the one you get isn't as good.  What you pay for is the knowledge that it will meet certain criteria.

Which boils down to - what is the purpose of the rifle?

Is it a plinker only?  Then go with the least expensive.

Is it for duty or self defense?  For that I'd want the best barrel I could afford so yeah I'd pay the extra cost.  

Is it for varmint hunting or competition?  You want an accurate barrel so an airgauged stainless would be very appropriate - nothing worse than a rifle you expect to be precise that can't turn sub moa groups with your handloads because of some relatively minor issue with the bore.

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Remember the barrel is the heart of the weapon, if you really want a good reliable AR you want a GOOD barrel.

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so while the more expensive barrel doesn't mention air gauging could it be assumed they are?  

For my own, which is still going primarily for plinking, I am going with a better barrel for sure but I was more interested in what I will be building for my wife which will be exclusively plinking and will see much less use I am sure, but I didn't want to get something that would be junk either.  I would guess at this point the less expensive one would work just fine for what she will be using it for

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Thanks, that helps quite a bit and generally backs up my basic thinking on it...however when the barrels are from the same company would it still be any real concern? Specifically I'm asking about PSA, they have rifle barrels in uppers that look to be the same aside from one showing to be HPT/MPI and the other to be lead-lapped and air gauged, there being a $50 difference between them.