Head Gasket change tips (experienced XUDers) please.

[Niall]

For the sake of £30 I'd sooner skim it rather than put it back together and it need skimming

That's just like changing the cam belt and not doing water pump because it doesn't need doing no brained really just good practice

Res engines will supply and fit seals if you ask Matt

No, its nothing like not doing a water pump. A water pump is a mechanical item which will wear out so yes, if your doing the belt, it would be silly not to do it. A head face will not wear out. If you have checked that the head is true when you took it off (which is easy) then why skim it? It can't get any better than perfectly flat. If anything, its going to cause more problems if its already been skimmed in the past in sourcing a repair gasket.
If its already flat, it doesn't need doing again. The only way it can leak after putting it back together and it was flat is if you haven't torqued it down properly and in the correct sequence. Oh and if you boil the tits off of it of course