Read what you purchase, lest you get distracted and purchase anew.
I would, of course, recommend sharp discretion over things that you pour any hard earned money into. With the internet being everyone's bosom these days ... you can get almost anything, for free. But ... from what I can tell, the accumulation of physical books today, is just a carry-over from centuries past -- it's a status symbol that doesn't mean so much these days, due to mass market publication being so fecund. It's a subtle notion because it's hard to recognize the habit, unless your person has immediate goals.
Books however can be passed on to the next generation, for at least a few hundred years before they need to be reprinted. If you have good taste, then most of a collection will be relevant for the next few centuries. I think humanity will eventually come to a point where "it" realizes that it's just circling around and over to notions that were mentioned by some far flung ancestors. Some hard evidence will be readily appreciated at that point, should we get to it.