Yeah I absolutely love the 20 but I just seem reluctant to use it. Could be it's age? Though some days it's perfectly fine. I love the focal length because it's not as 'regular' as 25mm or 15mm. I call 15 regular because I have this personal stigma against the iPhone focal length. But hey it was chosen for a reason and is versatile- I'm sure I could be happy with it.LOL, I love it! It really does go to show that for many people, zooms are often used at either end of the range.
A few random thoughts - Sounds like the 20mm AF is letting you down in the action shots situations? The 20mm used to be my main prime, but if the slow AF of the 20 is bothering you that much I like the 15+25 combo as a fast replacement. I started with the PL25 and really love its look, but over time I've found the 15 is a better focal length for me indoors/social or when I bring a camera along "just in case." Only you can say if it's too wide for the way you see the world - maybe 17mm would be a better fit? Depending on what/where you're shooting at 12mm, keeping the 12-35 may be sufficient instead of adding a 12mm prime.
It just comes down to I want to shoot a lot more, and after going through my collection I've had this realization that the primes do have this magic to them. I see a GX9/10? camera in the future and want to be able to take a prime or two everywhere. It would be nice if the prime worked well on my G9 as well (no OIS needed but fast AFS/AFC). Could all be GAS though.
I'd have a hard time justifying the 12mm prime, I can get away with a lot with the 12-35 and now even more with the crazy IBIS of G9.