Frankly, that seems a bit much. Given that there are
ways to reverse
that yellowing if it occurs (google "retrobrite" for more info), I'd
say that simply limiting exposure to UV is an adequate measure. If
things happen anyway, at least you'll know it can be fixed.
Does the chemical change that causes the yellowing have any other effect?
(e.g. does it make the plastic weaker or more brittle?). If so, can
_those_ effects be reversed? To be honest, I am not over-worried about
the colour of things like Vt100s, but I'd rather they didn;t start
falling apart...
-tony