Lots of people like the AR15. If you do, then stick with what you have.
As far as being quickly fouled, the PTR GI series have remedied the issue of tar sealed ammo. This is an issue which was a big deal 10 years ago when surplus 7.62 NATO was readily available. However this is less of an issue today considering that the South African, which was once so available and so inexpensive, has dried up. Also, at a dollar a round for present day 7.62NATO, I have chosen to handload my ammo, which solves the problem all around.
And yes, I have experienced the failure to extract issues after less than 20 rounds of surplus ammo in my rifle.
The headspace issues I *think* you are referring to is bolt gap. I say this as headspace on a Vorgrimmler action is not the same as it is on a rotating, or tilting, bolt action. I have read many accounts of shrinking bolt gap over the years. I do not know whether these issues have been remedied by PTR 91, Inc. They have treated me well, and been of considerable help to me with early issues with my rifle, even though it was built by the predecessor company, JLD Enterprises, Inc. I presently have +4 rollers in my rifle, and a spare set of +6 rollers in case it becomes an issue. The rifle seems to have stabilized at +4.
It is a mixed bag as far as the ammo you would shoot in it, and reports of recoil interest me, as subjectively, all 308's recoil comparatively. It is not severe, but it is no maiden's caress either. To ameliorate recoil impulse, the HK heavy buffer, which is available online these days, sort of changes the character of the recoil impulse, makes it seem less noticeable, perhaps more a push than a shove. I don't know.
It shoots the 155 Hornady bullets like a house afire. The performance of the rifle with ammunition it likes is astounding, and it is one of the reasons I don't see myself selling this rifle ever in my life. It is frankly just amazing. I've told the tale before, but I've shot prairie dogs on the run with this rifle at over 400 yards.
The rifle as it came was a good one, but as I alluded to in my first posting in this thread, the accessories and upgrades I have accomplished over the years with the rifle are what make it "mine" so to speak. -- The paddle mag release, ambi safety, trigger job, wide fore end, heavy buffer, Magpul stock, skateboard tape on the pistolgrip, Versapod spud and bipod, the Cooley Compensator for 3 gun, the Hensholdt 4x scope, the Bundeswehr scope illuminator, the monopod for the rear, all of these things have made my rifle suit me just fine. The 22 lr kit is a real score given the prices of ammo and components these days. I used to have the "blue round" bolt carrier and tried that ammo, but for some reason it just didn't work well in my rifle.
The $.50 magazines were a bonus, especially when considering the second to none robust nature of the build quality of these mags.
It is just a whole lotta fun. Unlike many here, I am not an armchair commando. I don't worry about blue beanies, nor meltdown of the economy or any of that sort of thing. I don't own a "fighting rifle" as in my neck of the woods, the only thing I am likely to ever fight is old age and boredom -- the latter of which, ironically, this rifle defeats handily each time I shoot it.
Good luck and may you be forever young.