Well, I find that, because you're really going for the oils in the peel, a lemon twist actually adds in just a bit of bitter, instead of sour -- which, again, is something that some people like in their martinis, but it doesn't do that much for me.

I don't know how port and gin would go. I suspect it'd depend on the port and the gin, but it seems like it'd be a bit of work to find a pair that worked well together. The other thing that would do would be to add a bit of color to the drink. Part of the appeal of the modern martini, to me, is its pure transparency, which is among the reasons I went with the rice vinegar instead of balsamic or cider.