I first read about this place in David Dekok's "Murder In The Stacks," the definitive story of the still-unsolved 1969 murder of Penn State student (and Holland native) Betsy Aardsma. Dekok goes into a lot of fascinating detail about mid-sixties Holland, and describes the Poe Club as a hangout for local Hope College students. I haven't been able to find any photos of the interior or exterior of the club, but damn - great name.
For what it's worth, Dekok's book is highly recommended. Take a look here.
As far as I have been able to tell, it looks like the weekly Grande ads disappear from the Free Press right around this time. There are scattered mentions here and there in 1968 and after, but it appears to me that the weekly advertisement for Grande shows in the local "straight" paper stopped - or was stopped - in late 1967. I can't help but wonder if this had something to do with the post-riot climate of the city, when the underground scene had been identified - and targeted - as a genuinely subversive element, rather than harmless fun for the teenagers.