you should be thinking about re-surfacing the cylinder head, however bear in
mind that there are only so many times you can do this, when the cylinder
head is removed the machine shop etc who machined the head last time
(assuming it has beed machined before) should have stamped a number onto the
surface to indicate how much was removed last time round. ( in the uk this
is normally stamped in thousands of an inch)
resurfacing the cylinder head also affects the compression ratio so this
should also be taken into account when purchasing replacement head gaskets.
its not so critical on petrol engines, and not even sure if thicker gaskets
are available for these engines, diesel engines however require thicker
gaskets to compensate for anything removed during machining.
if its a minor leak you could take a gamble and not bother with machining,
but undoubtebly it will not last as long.
but as the previous poster suggested you should always replace the cambelt
when it is removed for any reason.
regards.
Steve.

After the head is off, you can measure the amount of variation in the
surfaces (with a straight edge and feeler gauges) and determine if
machining is required at that time.

Why? One of my E30s has almost 200k miles and it runs seriously well.
Better looking than most of the cars that replaced it too.