Use joint compound over grooves in paneling that have already been painted ?
The flat paint will hide the most imperfections but, you'll need to spend the extra money and get a good product that you can clean those scuff marks. SW Cashmere. If you use a satin or especially a semi-gloss you'll see every imperfection on the wall. So I would'nt use the sheen for the cleanabilty here. And Bob's right those gaps are never going to be perfectand won't keep from cracking. So if that's the main issue here he's right remove the paneling. You don't need to sand the flat before painting over it but, you'll have to put a light sanding on the semigloss to remove the sheen before painting. Paint will pel if it's not a clean, dry and dull surface.