Great thread. The common perception is that older is better, but anyone who has read Jim Murray's Whisky Bible knows that not all experts agree. Murray often rates younger whiskies far higher than their older and more expensive bretheren. He seems to believe that there is an ideal age for some whiskies, and to surpass that is a mistake.
For my part, I have not tried too many whiskies beyond 12 years of age. The ones I have (Wiser's, Gibson's, Alberta Premium) are certainly better-tasting than their younger counterparts, so based on that I would conclude that older whiskies are often of better quality, in terms of flavour.
Then you have the question of diminishing returns. Is a 30-year-old Scotch really worth eight times as much as a 12-year-old? How is one to judge such things anyway? You are paying more for the relative scarcity of the drink than for the increase in quality.