Is it worth using IngramSpark as well as KDP Print, or is KDP Print enough on its own?

For most indies the sweet spot is both, but used for different jobs. Keep KDP Print for Amazon sales — it's free, and it prints your Amazon orders more cheaply and quickly. Add IngramSpark for everywhere that isn't Amazon: bookshops, libraries and other retailers order through Ingram's catalogue, and they generally won't stock a book that only exists on KDP because Amazon is their competitor. The one setting that makes this actually work is offering a proper wholesale discount (usually 40%+) and enabling returns on the Ingram edition — without that, shops can't or won't order it. If you have zero interest in bookshops or libraries and you're purely an Amazon author, KDP Print alone is genuinely fine and you're not missing much. The cost and admin of Ingram only pays off if you'll chase that offline/retail distribution.