MacLover, I agree with you in regards to Glenlivet and Glenfiddich. Particularly in the case of Glenlivet, where I personally found the 15-year to be superior to the 18-year.
Also, I don't know if it's a maturation in taste, or maybe because I find myself disliking heavily-sherried scotches a little more than before, but I recently poured myself a dram of Macallan 18 (bottled in 1985), which was - and still is - the most expensive whisky in my collection.
It has always my favorite scotch for the past 2 years. But as I was having the dram, I found myself thinking "boy, this isn't as good as I thought..." It was, well, in a word, too "sweet."
I think this stems from the fact that I find myself more and more drawn to heavily peated whiskies now...
However, I do remember tasting Highland Park 18 at a recent tasting event I attended, and while this isn't what I'd call "smoky" or "peaty" either, I enjoyed it immensely.