Well, I don't happen to own any tartan ties to match my kilts, but if I did I would wear them if I thought they looked OK with the outfit. 99% of the times I wear a tie I wear a waistcoat, so that would break it up OK for me. I do have a saffron tie, and have worn it with my saffron kilt that way.
I also have tartan flashes to go with a few of my kilts, and again, I'll wear them if I think they look good with the rest of the outfit. I can say I don't think I'd wear a tie-kilt-flash combo though, I guess that's my 'too much'.