| If you look at the most expensive basses (and some of the not-so-expensive), you'll find inserts used in places like the control plate over the electronics. I think it is most common when the smaller screws are required. My Kawai has 'em like this. IMO if you were to do a complete overhaul of the screws in your bass, you would not influence the value at all. It might even be a plus to someone that appreciates that kind of thing that you have done this type of work in the interest of keeping the screws and holes in pristine shape.
If you do this though, I would make a suggestion. Don't replace the screws with plated or brass machine screws. Use only stainless steel in conjunction with brass inserts. The problem is that plated steel will eventually begin to corrode the brass through electrolysis (corrosion between to dissimiliar metals) and eventually will lead to failure of the threads. As a matter of fact, I replace ALL of my screws with stainless steel since they will never rust, chip, flake, corrode, and always look good. You can even polish them to a nice lustre if you've got some that are well exposed like on a bridge or something. They aren't the easiest to find but keep looking. I happen to have a wonderful hardware store near me that carries all of the stainless steel screws you can think of - metric, machine, cap, wood, sheet metal, - all of 'em. I just go and by as many of whatever I need.
Hope this helps. | 
