I think it is a great idea, I guess the things that can occur with oldies are ingrained behaviours and issues from their long life, health problems (some can be very expensive), sometimes having to do the nicest thing for them quicker than you thought due to underlying health issues. Just some of the things that come with oldies.
That being said someone I know only takes on oldies and gives them a brilliant old age, she got a dog, she didn't think he would last long due to heart issues and mobility, when she got him she could only walk him down the driveway until he had, had enough, but now they go around the block a few times a day and is doing so well.
I would love to have oldie dogs but the heartbreak of losing them would get me every time and that would be too hard, it is bad enough fostering.