Just my two cents:
Like Stan said, they are entirely different. My Pono sounds almost exactly like like every Kamaka tenor I've played, and even though my 20's Johnny Marvin is a different size, the Marvin is much warmer. Honestly, I pick one up and play it and think it's absolutely the best instrument I've ever played, then I pick up the other and think that it's absolutely the best instrument I've ever played. They're so different, but they're both so great. I honestly think that everyone should experience owning an all-Koa ukulele and an all-Mahogany ukulele.
If you love your Kamaka, you'll still love your Kamaka. If you're looking for an "upgrade", then you probably should look at something different because, for what it's worth, I wasn't very happy owning just the vintage Mahogany ukulele and I think Koa is just such a distinctive sound that you just can't go without it. I think that the best option is owning something new and Koa for the contemporary uke sound (ala Jake and Eddie and Aldrine) and owning something very old and Mahogany for the classic, warm and rich ukulele sound (ala Johnny Marvin and Cliff Edwards).