For the most part I'm not as bothered by the extra instrumentation or weird rhythms that sometimes go into "folk" recordings. I just don't consider them folk music. It's really American Popular Music -- someone trying to make a commercially successful CD.
What really gets to me is the reverb that I hear from time to time on relatively recent recordings of traditional music. I find it really distressing to be unable to understand the words to a song because of an echo chamber. And it's also ruined, at least for me, some very fine underlying singing. If they'd left the reverb off, some singers would have had great records.