You definately need to come to Scotland for at least part of your trip - but not with a tour group, they're all very cheesy and usually full of really old people (nothing against old people, but knowing my gran goes on these sorts of trips, I would advise that they tend to see a little bit of the place they are intending to go, and then head for high tea, and go home... hardly the most in depth exploration of the country).
Best idea, in my opinion, would be to hire a car, get a good gidebook, or alternatively, a good Scottish person as a passenger, and cruise around the country for a few days, stopping wherever takes your fancy to stay and eat along the way.
This way, you can see what you want, but not be tied to a tour group...
Places I'd recommend....
Edinburgh
St Andrews
Glen Coe (on the way up to Fort William from Edinburgh)
Glasgow (maybe, it's more of a city with things to do, as opposed to the rich historic nature of Edinburgh)
Aberdeen/Inverness (if you have time)
Linlithgow (near Edinburgh, nice big palace where Mary Queen of Scots was born)
Stirling (Fairly large town with a very impressive castle)
Any more info you'd like, just give me a shout...