I have never heard a Luthier say the SSP enhances the sound of an instrument, only that it lets the player get better feedback.
Andy, you know I love them and have included one in all my commissions since getting one on my Boat Paddle ML. But that is neither here nor there as a few commenters have mentioned, such as no longer playing in a group and therefore they can hear what their playing well or playing the uke most of the time through an amp so no need for it there either. When I play with the group, I really can tell the difference, say between my BP with a sound port and my MM without a sound port. IMO, even when I play at home I still prefer the SSP, but that is only my opinion.
I recognise your conundrum though, adding all those nice optional extras can quickly double the cost. I'm facing the same challenge with my up coming Beau Hannam Players model. I have added so many extras and want to add a few more before Beau starts, I feel I might as well go all in and just order his next price level instrument. You only live once and I can afford to go on a diet and not eat for a month or two. That's one strategy for getting slimmer and owning a better instrument at the same time. lol