Perhaps not exactly what you are asking, but my grandfather collected antiquarian books. It was quite the collection and even had a first edition of Alice in Wonderland with beautiful colour plate illustrations and one book that looked like it had been signed by Queen Victoria. My mother had previously sold a miniscule little book of (I think) Patrick Kavanagh's poems for around £1000 or £2000, but had opted not to sell the Lewis Carroll because it was so beautiful.
So one summer, many years ago, she tasked me with valuing and selling off some of the rest of these books that had just been collecting dust under their bed and I hopped online to sites like Abe Books, made a little spreadsheet, then set off with a rucksack of what I thought was around €1000 worth of books. Now, as I was quite young and unemployed this seemed like a lot of money.
Alas, my first few trips to various bookshops specialising in this very thing were all futile. I eventually managed to sell a few but for much less than I thought, and to get anything reasonable I ended up having to part with the Alice in Wonderland. Thankfully I read it before.
This is all to say I would not recommend investing in books. They take up a lot of space, gather dust, are not particularly liquid, and most won't even appreciate and you've got to be careful not to damage the ones that will. Anything less interesting than a signed first edition by a renowned author will barely even get a second glance.