Can I lay peel and stick tiles over existing, old vinyl?
NO- Peel and stick vinyl is a trap! Glue-goop seeps up from the seams after about a year, making black blobs on the floor (to clean, scrub with a putty knife, weekly at least), while at the same time dirt begins to find its way under the edges of the tiles and then the corners begin to fail, peel up, and crack. If you get any dirt on the goop underneath the broken tile the floor, it's awful to try to get it off. You can peel the whole tile off, but you will never clean off the goop/glue, so you really can't take them off; and you can't add new/more vinyl on top of the peel and stick tiles either! Once you put peel and stick tiles down, there's no return. You'll have to pull up the first layer of vinyl and remove everything before you can add something else (because the peel and stick tiles will eventually peel up).

NIGHTMARE!