I recently bought the 270EX II to use with my G9 and G11. It's a lot smaller than my regular 430EX II, but also much less powerful. The 270EX II is certainly much easier to carry with me, and "fits" the smaller bodies well. I also have the Canon off camera cord, and the ST-E2 wireless controller. The 270EX II works with either option, including HSS.
I still prefer the 430EX II over the 270EX II, because of the added power, swivel head, and other features. But, it's much larger, and taken with me less often. I like to be able to use a flash in daylight with HSS to shoot macros or close ups of flowers, bugs, etc., so I'll bring the OCC or ST-E2 and a flash. The 270EX II will be my go to for this, because it's so small and easy to carry.
If you go with the 270EX II then an OCC would be the less expensive method to expand/improve it's uses. But, it cannot throw as much light as a larger flash.
Dennis