Bookshelf vs diffuser panel. Who wins?

@fleschler 

Sorry to hear your story. Love to see your systems and venue.

You may have heard me talk about my room. I just really lucked out with incredible acoustics. Large highly asymmetric room. 

Guys: as with everything in life, there is no free lunch. Bookshelves, rags, towels, blankets… you name it. Been there done that. There is no substitute to real room treatments. Let’s not fool ourselves. Yes, we all want to save money AND effort/ work.

Good diffusers will be much more effective than bookshelves by producing a 3-dimensional airy sound in the midrange and treble. That’s the main difference when introducing diffusion in the room.

Sound-wise diffusers will win. Practicality and aesthetically bookshelves have the advantage. Although they might not bring a large impact as proper diffusers, they still bring some and it's better than none. On the scale of 10, if diffusers score 9, bookshelves score 4 or 3. Better than none.

How about a few big towel racks on the wall. 
 

mr fleschler, awesome info about your book collection.  My mother had lots of books and she gave them away to the library.  To my horror she gave away lots of signed books.  I'm sure many were first edition really nice.

It seems in the 30s and 40s lots of authors signed many of their books I guess.  I have four books signed by Carl Sandburg.  He liked Lincoln a lot. 
 

Horrifying experience to treat your room. Maybe it's OK now

@jumia 

I also acquired/rescued 40 lawn bags of books from the estate of the late Universal  pictures conductor Joseph Gershenson which were left out in 1988 for trash.  I took the 1,000+ books, donated half to CSUN (many were 1st editions/unsigned) who sold them at their book sale fundraiser.  My late former wife created the Friends of the Library there so it was a very appropriate donation.  I kept the music and history books. 

Glad you kept the Sandburg books.  For my late former wife's last birthday, I purchased the only remaining seven years (1916-1923) of the Owensmouth Gazette, bound by the former owner, Edgar Rice Burroughs (Tarzan author) who also founded and lived in Tarzana, CA.  Since my late former wife was the historian of the San Fernando Valley (she had three urban archives exhibits, one on line by the Getty Museum), president 10 years of the SFV historical society, this was the greatest gift I could give her.  Unfortunately, she died (after an 11 year systemic lupus illness) a few months later.  I then had the Huntington Library make a negative and positive microfilm copy which I donated to CSUN.   

Unfortunately, university libraries have greatly diminished book collections, at least not on the shelves, whose spaces are now occupied by banks of computers.