After the skirts have deteriorated on a buzzbait, or spinnerbait for that matter, has anyone ever fished them by simply threading a curly tail grub onto the hook?  Has it worked for you?

On a related question, is there an easy way to get new skirts into buzzbaits and spinnerbaits, or is it simply not worth the effort to replace them.

Well, personally, I always use a curly grub (or ribbon-tail worm) trailer - WITH a skirt.  I guess I've never really tried them without a skirt (and just the tail/trailer).

Not sure if I understand the 2nd part of your question as I've always thought that the skirts are pretty easy to replace.  Just remove the old one (cut/pull off) if it's still on and slide on a new one. 

Most of the replacement skirts have a small surgical-rubber tube at the core.  Just carefully slide it over the point/barb, around the hook bend, and on to the head "neck" - just in front of the hook.  If you have problems with it slipping off, use a drop of instant-glue.

Hope that helps...