My reasoning was that if I could make the kilt seem that much more professional then the powers that be would not be able to say anything.
That is exactly what I'm going for too.

Thanks very much for the input! That helps, I think. Judging by the examples posted in the "10 looks" thread, I'd probably be going for somewhere between "day wear" and "smart day wear". So I suppose a waistcoat would be in order.

Waistcoat length depends almost entirely how you wear your kilt and where it was measured from. For example a traditional kilt will be measured from above the belly button, modern style kilts, I am led to believe, are usually measured below the belly button. The trick with the kilt and waistcoat is that there should be no gap between the two. So however your kilt is measured, think NO GAP with the waistcoat! Just one last thing to bare in mind is if your waistcoat is too long your sporran will not hang tidily in place.
Good advice. My kilt is measured to ride on my waist, above my belly button. So I'm not worried about a waistcoat being too short. If anything, I'll have a hard time finding one that isn't too long. I'll look around, though, for a decent one.