As I said before, I really don't think that particular library will be closing any time soon. There have been some changes with the Camden Libraries, but I haven't heard of any threat to that one. It's usually pretty quiet in there too, at least at the times I go.
What would put me off buying ex-LA are potential unexpected demands for large amounts of money.
On the other hand, I wouldn't buy a flat in a converted house like the Priory Rd one either. They look nice, but the lack of sound proofing in SO many conversions makes living in them a horrible experience.
I've been in loads of friends' flats where you can hear the neighbours coughing, boiling the kettle, turning light switches on, practically every word of conversations if they don't know how to use indoor voices... And that's ordinary day to day living, thats before they put the music or TV on loudly!
I have a friend who lives in a top floor Victorian conversion (actually that's also in Kentish Town) and you can hear every single sound from the flat downstairs so it's not just living on lower floors that's a potential problem.