Hands down YES! I won't buy another new uke without one, of course there are some great older ukes before SSP's were being done and I wouldn't pass up something with a different voice because it was made before SSP's. As everyone has said (who has one), the sound difference is game changing, kind of like listening to your "no SSP" uke from above while playing it, then standing in front while someone else plays it... whole different voice! I can't imagine when I would want to slide a cover over my SSP so that is an option I wouldn't pay extra for. No downside, and I love being able to see the insides of my uke without a mirror. I have built a couple ukes and a guitar and put side ports in all of them (sounds great on an acoustic guitar as well).
A side story, I've heard when Augustino LoPrinzi was experimenting with his acoustic guitar builds, he put sand on the guitar top and strummed the strings to see where the "energy" was focused and found the sand danced on the 2 sides of the upper bout. So he cut out a slice of the top and side on both sides of the strings, and the "Nova Model" was born. He used it on both Classical and steel string acoustic guitars and later on ukuleles. I've had 2 tenor Nova's, one spruce top and the all Koa I still own. It does make a difference and is kind of like a side port, before SSP's were a thing!