Last summer I got a consistent 53 mpg with my '11 Wee - and was quite satisfied with that.
The last month or so, closing in on 30k miles, I'm averaging 57 mpg. I'm calculating full tank to full tank every time.
I've been keeping the tire pressure up to 40/36 front. The rear is over half worn currently. I have stock gearing.
I've also been inadvertently using the lower end of the power curve. Whereas last year I'd cruise at between 4,500 and 5k rpms, I'm finding plenty of power at 4 - 4,500 rpms, rolled on progressively, and of course less in the lower gears. So I'm using 5th and 6th earlier and more frequently. I haven't been trying to save fuel either. I just hadn't realized there was power there before. True, its a tad more "relaxed" there, but unless I'm accelerating out of twistiess, I feel no need to run at higher rpms.
The other thing I did was add about 5 ounces of Chevron Techronic injector cleaner in a few tankfuls. Maybe it was a coincidence that mileage started improving then (and, yes, I did calculated the additional fuel it provided)
Lastly, I used Mobil 1 last oil change (for info: I doubt it had any affect)....
Likely, they were all contributing factors but I'm very happy to be getting the upper end of 50's mpg.
Just another reason to feel the love!