Not sure I'd personally go for a black tweed. I consider tweed primarily day wear regardless of the colour. If I wanted to wear an Argyll in the evening where others were going formal, I'd personally go for barrathea.
I think the level of formality of the particular supper determines whether a tweed, barrathea or black tie look is appropriate rather than the fact that the PC attire is a "new invention". Charlie coatees are almost 100 years old and derive from the Regulation Doublet which is older still and besides, Burns didn't wear a kilt anyway, so it's ok to live in this century and kilt accordingly.
I agree that those of us of Scottish descent will always pass an opinion, so this is mine. 
I have a lovat green braemar day tweed, a Prince Charlie coatee, a velvet single breasted montrose doublet (kind of like a GT doublet) and a barrathea bottle green kenmore doublet. So I'm good for smart day wear and very formal but I'm missing a barrathea argyll/braemar/crail/wallace for those in betweeny evening events that are a little too refined for the rugged look of tweed but not quite black tie. Since the tweed is considered a business suit equivalent, I can certainly wait for the right deal.
Which would I wear to a Burns supper? It depends on who was hosting the supper and what the invitation called for.
Natan Easbaig Mac Dhòmhnaill, FSA Scot
Past High Commissioner, Clan Donald Canada
“Yet still the blood is strong, the heart is Highland, And we, in dreams, behold the Hebrides.” - The Canadian Boat Song.
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