So I went for the regular service at 15,000km. I replaced the spark plug, oil filter, oil, belt (I didn't go for the original one here, bought Powerlink's 22.5 x 906),transmission oil and air filter. I also replaced the whole front pulley (variator) assembly. Changing the belt and the variator assembly hasn't resulted in anything - the bike has as slow pick-up as it did, and is still really unpredictable at launch. The mechanic said it might be due to the EFI valve. I found that on taobao and will probably replace it come next salary.
I am indeed very interested in the result of that. Another plan for the next salary is to get a fatter tire to smooth the bumps out and to replace the whole rear brake system. It looks like there have been 2 variations / revisions of the Jetmax, and the only rear brake pads I can get from taobao are for the newer version. My bike apparently has an older version brake caliper.
Will post updates as they come.