Those scotches---actually, single malts---that you're drinking are already pretty classy, Glenn.
And I'm with Tom NJ: that 10-12 range is pretty darn reliable for good quality malt. Truth told, for me, it's fairly rare that you get over 15 that single malts remain all that interesting. Won't turn them down, mind you, but where Macallan (the Sherry, not the Fine Oak) is great at 12 and sublime at 18...I don't care at all about the 25.
My one standout with age...and it's a lovely experience when you can taste them side-by-side---is the Highland Park range, the 12, 15 and 18. The HP 18 is my idea of the best possible single malt. It's one of the rare special scotches I'll actually deign to spend my money on. (On the other hand, the fact that the west coast Highland Park ambassador is a buddy of mine comes in pretty damned handy for my spirit larder.