Buddy of mine went to see Roth and Hagar on their combined tour a couple of years ago. He said that Sammy hadn't lost a step (and actually, was better than with VH). Also said that Roth sucked. Not only did he sound terrible, but he forgot the words to one of the songs.
Age will do that to you.
I've repeatedly heard and/or read two completely different accounts of that tour. One version is the above; the other is the opposite scenario. Not surprising, given the way the fans tend to polarize over that issue. I thought it was a ballsy thing for the two of them to do, knowing that on average, half of the audience would be there mostly to see the other guy. I respected them both a bit more for making the effort.
Eddie Van Halen, on the other hand, recently lended his guitar talents to the soundtrack of a porn flick. There are clips on YouTube.