Well I tried the intake cleaning white spirit method today.
I used RON ECHT's method as shown in this vid
I took pictures with the borescope before and after. It was hard to get the scope in but I did my best, here are the results:
Before
After
Admitadly I only got one valve but there is clearly a reduction in carbon. On the road the car feels no different so far but at idle the is no more puttt noise as it ticks over.
Like Ron I think I will now be doing this periodically as its very easy to do.