I agree with you that sites should be accessible to all. What I mean with target group is not a group of people with a similar impairing condition, but similar interests. Eg. a group of software engineers will probably search for the "re-size text" option differently than a group of linguists. And with seniors it should be as easy as possible to find it, and be non-obtrusive otherwise.
Mind tho, this is coming from someone who "designs" web-pages as black-on-white, default font & size, should be readable in lynx or w3m