Good ear — “Valerie” has a wicked solo, along with some great fuzz work during the verses. I just don’t recall which session guy played it. I’m pretty sure that Glen Campbell was through with session work by then, so I don’t think it’s him.
I knew that, when the Monkees began, the music was pretty much .. if not completely .. performed by session musicians with the actors going through the motions. But I thought that, by the time Valleri was made, Michael Nesmith was good enough to have done the solo.
However, in going to Wikipedia, I found this:
The original recording (with instrumental backing by the Candy Store Prophets, plus session musician Louie Shelton contributing a flamencoesque guitar solo) was featured in the show's first season in 1967; a staged performance showed Michael Nesmith copying Shelton's guitar licks ---
Live and learn, I guess ...