It has been suggested that the 'uncarvable' stone used in the Carrowkeel passage graves may have been painted, but no direct evidence has been found. The conjecture comes from the Iberian examples which still have 5000 year old paint on them.

There was a huge wooden pole in the centre of Navan Fort in NI. Would you just erect a 50 foot tree trunk and leave it plain? Maybe, but odds are that it would have been decorated somehow. Then again a 50 ft pole is pretty damned impressive in its own right.

I think you have to look at the area you are in. Ireland and the UK was glaciated and there's a lot of eratics lying around to use. No need for quarrying.

Although many Bronze Age wooden things have turned up in the Irish Bogs there are not many earlier things.

A few carved figures (just 3 or 4 foot high) have been recovered. As an aside, these have dowel hole in the groin, possibly to slot in a huge ... erm ... right ... is that the time?