My '81 uses the same headlights.  When both are the same age, and one
burns out, the other is bound to go soon also.  When they reach 'old'
the inside reflective surface has decayed quite a bit and does not
reflect as well as it use to.  The  bulb filament has also decayed so it
isn't putting out all the lumens it use to.  Normally you can see quite
a bit of difference in the color of the light when looking at it.  The
new one is bright and the older lightbulb is yellower/dimmer.  So I
suppose it comes down to just how well you want to see, as to
whether/not you feel the extra money is worth it.  One good thing to do
is pull the power cord to the lights and make sure the contacts fit
tight and are clean.  Lots of dirt in/on the terminals can cause a less
than perfect contact to the headlight terminals.

Dave S(Texas)

   It is a very good idea. If nothing else, when the new ones get older and
one burns out you have a spare to use till another burns out.

   It is probably half marketing, half security and common since. It winds
up being totally up to you, the owner of the vehicle. But remember, you are
on the road with hundreds, thousands, millions of other Men, Women, and
Children...is a human life worth the few extra bucks, it could be you or a
loved one!