Thanks for the info guys.

Re prices for unsupported poles; I was wondering about using either a cast-off windsurfer mast (surprisingly tough, but tough enough???? dunno) or perhaps a 49er top section which can be found around the yard at Woollahra SC fairly easily! Sounds like it may be too big and heavy though. Perhaps one way to reduce windage would be to have the stays connected to the tack; they would go out only when the tack was pulled out. They would not be as tight as a pre-set system, but does that matter? Lots of dinghies have flexy poles which they say flattens the kite when overpowered.
I think we may just bag the kite. Wouter's "all opening top bag" sounds good, just like the ones we use in Etchells and J/24s and I can drop them pretty quickly - and reliably. If you can bag an 18 or 12 footer's kite a 17.5m should be easy. Any comments?

While I know the Tornado uses snuffers etc, they are a much bigger boat and the windage/weight concentration issues may be of a different order.

I've often asked MG & NS sailors why the MG has (or had) a slower yardstick. From what I've seen it's related to the standard of sailing (having raced against the best in each class nationally), the fact that MG gear is developed from the NS which is (or should be) a very different boat in many ways, and the fact that on underpowered boats with trapezes, the average skipper tends to bear away in the lulls rather because the crew is too slow moving in. The weight of the kite and pole doesn't seem to be a major issue. And the MGs do seem to be going quicker nowadays, with assys.