dont really have to have it skimmed. only if the head has been overheated and is warped.
the 16v head is just really good design out of the box, thats why gains are minimal and very expensive. Having said that a small clean up and smooth out with not do any harm.
Dave franczak, or his dad would do light head work and porous repairs for very reasonable price, they run a business called v-tuning. I know a couple of people on mig who have had porous heads done at v-tuning and they are happy.
A m8 has just ported and polished my head for my 1600 Corsa, and also re-built the bottom end with oversized pistons, lightened and balanced crank, etc.
He does a top job and doesn't cost the earth - he's just started his own garage up in Lincoln. Give him a call....01522 568568 and ask for Fozzy.