I've printed a couple of spools at different sizes, it's really kind of nice to have them. Particularly smaller spools for smaller sample lengths, super worth it.
But another thing you can do is just print a little single-wall cylinder that friction fits inside one of your existing spools, then cut the existing (non-printed) spool in half down the middle and use the cylinder as a friction-fit sleeve to hold the two halves together. That also gives you the same functionality. It's not as cool but it saves on filament? ^_^