The Oly 17/2.8 and Sigma 30 are both small f/2.8 lenses that do great work. Being f/2.8 keeps them small and I like it that way; the 12-60mm zoom can handle the tasks when versatility beats speed and best-possible image quality.
However.. the appeal of the newer Sigma 30/1.4 was beginning to get to me! Events that really could use faster glass have come and gone, forcing me into the higher reaches of ISO to pull off. The Sigma small-30 has been a great fit for many reasons, so seeing it under such pressure is sad - but it was a good candidate for replacement with a faster lens. The Sigma f/1.4 is still pretty new and in demand, so used deals are not likely at all - and it adds more cubic inches and 100g to the bulk of my kit. Not unreasonable, but still less convenient than the little f/2.8 version.
The pressure has now been relieved - but not in the way I had expected.
This is perhaps the original 'must-have' lens for the µ43 system, with compactness and great image quality offset only mildly by a 'slow' AF system. I've offered up a few other spare parts in exchange so the final expense for it should be quite small.
One of those 'spares' is the Olympus 17. I'd be very hard pressed to differentiate between times when the 17 or 20 would take precedence, so better to skip that part. Thankfully the odd 46mm filter size on the 20mm matches the Sigma 30 (and their 60/2.8 for that matter) so a new pile of filters will not be needed. And on the GX7 the little primes are stabilized!
I plan to seek out a Lumix 14/2.5 in the future* for wider shots. That one is another early model semi-fast pancake that I've owned before and felt good about. That leads to 14-20-30 and 45-150 for the tiny kit, with the 12-60 for handy wide zoom. Turning the 14mm vertically and stitching 2-3 images would cover to perhaps 9mm for those rare times when that would be of value.
Here's a 'blog post from someone who looks over the Lumix pancakes and has enjoyed them for a while!
* some slight risk that a fisheye will appear instead for the wider shots.. we shall see..