Corrosion attacks more than the bodies of our beloved 914's (as well as many other European cars of a certain age)
Attached is a couple photos of a destroyed relay board caused by not replacing fuses and maintaining the fuse clips. The fuse board in the interior is subject to the same fate. As far as the frequency to replace fuses, I believe it mostly depends on how and where the car is operated and stored but certainly all cars need, at least, the fuses rotated in the holding clips regularly.
Keep the covers on, replacement interior fuse board covers can be found at 356devotion.com Clean the contacts with sandpaper or a Scotch brite pad, a VERY lite coat of dielectric grease (rotate the fuses after installing) and slightly bend the lower clip to maintain proper pressure.
I honestly believe there would be no need to "update" the fuse board if the above instructions were adhered to. Brad