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Even with closeup lenses I've not been able to get a proper macro with the G1X, how close can you get?
I think you had a G10 previously, so using that comparison, with the 250D (4 diopter) you can get "closer", more magnification, than the G10 with its native macro mode. Not true macro but great for flowers, beach pebbles and slow bugs. At minimum focal length a little over 2" from the front of the lens and at maximum focal length a little over 6". With the 500D (2 diopter) your minimums would be about twice as far, but its also a useful filter. I also really like the lens mount filter adaptor compared to the G10's body adapter. I have a neoprene sunglasses case to hold both the polarizer and the diopter each with its own adapter. Very fast and convenient.
As you said, its a quirky beast and you have to practice a bit. Its large sensor is a blessing and a curse, the DOF can get really thin and you often have to stop down to control it. With my G10, I took close-ups of peach tree blossoms and can still, unfortunately, make out a trash can sitting 20 feet behind the tree. Focus can be a bit dodgy with the 250D so make sure the focus area is of high contrast and it helps to physically move the camera to get the focus close before engaging AF. It often takes me several tries to get it to lock. The IS works well and you have clean higher ISOs (compared to G10) to stop down and keep shutter speed up, so with the articulated LCD you can easily hand hold down and under to see things you couldn't with a real macro lens on a DSLR.
I've always viewed the G series cameras as supplements or alternates to my DSLR kit. They can do things that are awkward or expensive to do with a DSLR and at just over a pound their great for backpacking. The IQ of the G1X is so good that I now have no qualms about using it as a second body to my 5D when it has telephoto, 17-40, or macro attached. Remember the Luminous-Landscape "I'm not kidding" article about the G10? I think it was a bit premature, but applies completely to the G1X.