Given that many age-related diseases are just the results of a lifetime of wear and tear ... understanding the aging process is very important. If we understand aging, it helps us understand things like cancer - or perhaps we need to understand cancer first, since developing cancer is pretty statistically inevitable if you live long enough. Certain diseases like Alzheimer's are different, and also not very well understood. We think it's similar in mechanism to a variant version of Creuzfeld-Jakob (the human version of Mad Cow, also called vCJD for short) but we're almost positive that it's not actually contagious at any dosage. It has hereditary leanings, but like everything else, you're not guaranteed to get it even if both parents develop it.
But things that we spent hundreds of millions if not billions of dollars on ... liver spots. Sagging and thin skin. Greying hair. Osteoperosis. Losing teeth. Fragile bones. Settling cheekbones. Why not combine them all and research the root cause - essentially, getting old?
The thing that people need to understand is that there is not a 'limit' on scientific research. There is only limited funding, limited manpower. The limits are externally imposed - and there is enough money in the world that if we take on the attitude of researching science once again for curiosity's sake instead of what's 'worth our time', we will benefit much more. If we get our children interested in science and encourage it as something based on smarts and not on your economic status. If we adopt the idea that not just 'rich kids' become scientists, but people who don't have Mumsy and Daddykins to support them through twenty years of post-grad... Some of the most ubiquitous modern conveniences were discovered in the course of other, unrelated research... there is no corner that is not worth peeking into when it comes to the world around us.
*blinks down at soapbox* Oh, hey, how'd that get there? Erm, 'scuse me. *flees off into the night*