Have the good people here tried this and is it easy-ish for a newbie? Some of the treads are quite worn (at the edge/middle). Can the cladding go on top of worn treads or do the treads need "filling in" first? (or would a quick sanding down do the trick?) Does "filling in" mean cutting out the worn section of tread and replacing it? Your honest opinion is most welcome, thanks
You need to keep the risers regular so anything you clad the goers with has to go over the top floor as well.
There are laminate systems for stairs which include items for the treads, risers and nosing. Not a great fan as laminate can be slippy at the best of times. trying to resurface a stair tread is not the easiest of job and has to be done by removing and replacing the tread from the back. If you don't get it exactly the same it will not only look odd but feel strange under foot. It would be best to post some pictures so we can see the extent of the wear
If the treads are MDF have they started to bend when you step on them? If so, it is probably best to replace them. I don't think cladding the treads is going to be very successful.