This is really fun, low cost and safe motorsport, and MX5s seem just made for it, with low weight, excellent visibility and ability to handbrake turn. And let's face it: how often do you get to do two dozen handbrake turns in an afternoon? This is a very different experience to a track day. There seem to be three or four regular MX5 punters. Try YouTubing willowbank motorkhana mx5 to see some vids of fives in action.
You can take it seriously if you want, but more likely you will have a good laugh as you disappear into a cloud of your own smoke and realize you have WD'ed. AGAIN!

The HSCCQ are a friendly bunch, and it is quite family friendly. Last time I was there they were running two courses simultaneously so the action was fairly continuous. Sometimes they run three courses simultaneously.
You can enter at the HSCCQ website or on the day. You do need to be a member of a CAMS affiliated club such as MX5CQ and need a CAMS license (a 30 day license can be purchased on the day if you need). A helmet is required if you are driving a convertible (soft or hard top).
For full details visit http://www.hsccq.com/upcoming-events/come-and-try-motorkhana/ a bit closer to the event.