For your agenda:

Chiang Mai Bike Festival 2014 (เทสกาลรถถีบเชียงใหม่ 2557) Chiang Mai Gymkhana Club. 14-16 February, 10 am - 9 pm. Contact [email protected] or 054 441 208 for more details.

Looks like there's another one this year (or did the last one not happen?)

Chiang Mai Bike Festival, Dec 5-7 2014

CMU Art Center (on Nim)

9am - 9pm daily

Anyone know if it's worthwhile from a 'buying new gear' standpoint? If it's just promo stuff and 'fun rides' I'd like to know so I can pass.

A better time of year than the beginning of hot / pollution season.

For someone who ever visited a "real" bicycle fair it's not exciting at all. No producers, neiter of bikes nor parts nor accessories. Dealers only. Most booths are offering fashionable stuff (as e.g. fixies in zebra or cheetah look, foldables, clothes, blue and green LED lights flashing in all imaginable rythms) at prices far above average and reason, and not willing to discount. Almost no technical innovations a serious rider could be interested in.
Good for a one to two hours stroll if you're already in the area anyway and havn't anything better to do ...

If you're interested in a birthday gimmick for your neighbour's pubescent son you'll find just the right stuff; if you're interested in any serious purchase you would be better advised to visit some recommended dealers and study some magazins/internet forums.