Well, as I live in Virginia and was here when HM The Queen came last year I would love to see Charles and Camilla come to my great state as well! I'm sure that President Elect will issue a gracious invitation as did President Bush and hopefully we will see them entertained at least in Washington with full ceremony (that means tiaras and orders!!)
I do agree that Charles and Camilla should visit Australia, and Africa certainly. Brazil could be interesting, and Spain, of course. It's a beautiful country and I can't think offhand of a time Charles has been, although I'm sure he has.
Charles has been a couple of times to Spain but only briefly in the 1990s & a few years ago for Felipe & Letizia's wedding. The last time he made a major tour to Spain was way back in 1987 when he greatly enjoyed his visit & he particularly impressed those he met with his charm and kindness - I was told this by someone then at the British ambassadorial residence.