I have had several Ponos--concerts, sopranos and tenors--and they sound similar. Not precisely the same, but super close. Just like your instinct is telling you: the differences are subtle for sound. And they feel the same, same neck, same basic weight, same weight distribution, same bracing system, same tuners (unless you get a different headstock), same strings, same soundhole, etc. Unless you get a professional sponsorship from Pono, why do it? LOL
If you are asking if you should go with another brand for your second "quality" uke, Ice: I would.
Completely different in sound and feel are Martins, Mya Moes, KoAlohas, for instance.
If I were trying to find a different sound, even though I truly like Ponos (except for the necks), and still to this day own two--a slot-head maple tenor and a 'hog soprano--I would definitely get something different.
Honestly, you might love your car--but do you own two of the exact same models and years of that car? Well, actually, I do: my wife and I have his and hers Toyota Sequoias, same year. LOL. So, you see, I'm one to stick with what I like...and even I would get a different ukulele if I were you. lol.
I strongly encourage you to get with your local ukulele club, travel to Mya Moe, hit a store (some great ones in Eugene, and all over the state, I see on Google; and Neil Chin is at Pacific Winds now; he's amazing!), or befriend locals from UU and try their instruments. You have many threads on UU asking many questions (which is fine, btw), but if you haven't noticed by now, everyone's opinions differ, none match yours precisely, and most questions about sound cannot be put into words. Try some ukes, brother Ice. Try some ukes!