Just visited 15 distilleries in the last few weeks. Admittedly, I am a scotch novice, but I can say that the premium tours we did take were worth it.
A couple points which you might find useful:
- The smaller distilleries have much better "Free" or "standard" tours than the big names. Kilchomann let us look inside the stills since they were being drained, taste the wash, and take photos of everything. We even talked to the stillman for 10 minutes and asked more in-depth questions. As you noted, the tour at Edradour is a classic. It's designed for big groups, but they do a good job. Bruickladdish is also an excellent standard tour, and their distilling setup is a bit nonstandard which is interesting to see. (using really classic machinery to make some really modern spirits... octomore, etc...)
- The premium tours are certainly "worth it". (I wish we figured that out earlier in our trip.)
1) We did the "Exculsive tour" at oban which was about 25£ with our discovering-distilleries passport. The group is small, they took more time for questions and the tastings were nice.
2) Laphroaig offers a "premium tasting" for 25£ where we got to taste some excellent hard to find expressions. I didn't do a tour, which was fine since after awhile the distilling process gets memorized, and you get to the point where you can give a better tour than the college student working a summer job giving whisky tours.
3) Lagavulin offers a £15 "pre dinner tasting" which also included great expressions, but they are paired with food.
For more info on our trip and my takeaways about the overall scotch whiskymaking process, take a look at this article on my blog that I just wrote... It has lots of photos from many of the distilleries you are hoping to visit.
enjoy your trip, and I hope this helps!