I read 5-10 books a week so I put yes if I can afford it.
I rely heavily on the library as I have always done and I reserve books in series order if possible but there are only 5 holds allowed at my library.
I do buy books, but my disposable income is not high (retirement looming and savings more important)
If I see a book I haven't read that is available and sounds interesting I get it even if it is number 14. Especially an unfamiliar author. Then I know if I am interested in reading the whole series.
Lucky for me most series I enjoy do not contain spoilers or rely heavily on knowledge of back plot.
And if times are tough I will read almost anything
Helen