I guess what you need to consider is the pros vs cons of upgrading.
An SLR based system will make it easier to get better images, but it is a more complex and complicated animal. Understanding settings will still be a prerequisite to getting the images you want.
If you feel that you have exhausted the creative potential (for you) with the G12, it is definitely time to move on....
My feeling is that the G16 will probably produce marginally better images, but will not be a huge leap over the G12.
My only other thought is that if you are finding that camera settings and figuring them out is a challenge, perhaps try and get on a workshop or hire a pro photographer for a few sessions. This will also help you decide whether the upgrade path is one that you wish to embark on.
All the best
This would echo my advice. I think you say/admit that you are not exhausting the potential of the G12 since you see much better images taken with it. Instead of spending thousands on new gear, spend a few hundred and get some one on one advice from a pro. I did this a couple of years ago and besides the money I spent on my very first P&S housing, it was easily the most effective money I spent to improve my photography. I too did the G10 -> G12 -> G15 route and the gear made, at best, a minimal difference. When I did finally switch into a u4/3 system, honestly my images suffered for a trip or two until I learned my *new* system.
If you are having trouble taking the images you want with a G12, you'll struggle with something "better". Sure, some things become a bit easier, like focussing, but I'd really suggest you try to milk as much out of the G12 as you can and identify a real shortcoming of it that's holding you back before you spring for something new.