Are there some vises which are more valuable unrestored ? Found an old Athol #72 which I've never seen before and am questioning restoration or leave as is. Think it might be pre-1905.
I don't think they are like guns yet, but maybe leaving original paint and pulling it apart and cleaning it up is a good idea. put some nice lubricant on the moving parts and maybe wax it so it doesn't rust if it's not a daily used vise. also depends on the rarity of the vise if you should paint it.
Most any vise is worth more in a cleaner working condition. Now if you want one to look like the green Parker that is sitting on Ajchien's workbench that is definitely worth more than one that is not restored you might want to figure out how much your time is worth.
if you love it and are going to use it and look at it all the time does it matter that you spent a couple hours painting the white letters? or painting 2 or 3 coats of paint after a nice prepping? you probably made minimum wage for your time if you ever wanted to sell it. did improve the value? sure you did. in the meantime you have some nice vise **** on your workbench.
now a 1700 or 1800 made vise that hasn't had too much abuse might only need a good lubing and waxing if you don't plan on keeping it in a heated area. just because they are less common and parts are impossible to find will up their value as time passes if you have a working one.