"So on the Craighouse Road/Balcarres Street Craighouse Gardens work, how much more would it really have cost to put in red tarmac rather than just red chips."
Well quite.
One problem is that most bike and bus lanes are laid down as an extra coat and have to be relatively thin. If the road surface isn't prepared well there is the extra chance that it will come off in lumps even before it 'wears out'.
BUT the real problem is that fixing such things would come out of the revenue budget - which is never big enough to deal with all the repairs.
So things get worse until it's time to redo the whole road (capital budget).
"Surely the cost of resurfacing a road is in the scalping, the labour the plant and so on. Yes sure red tarmac costs more, but in the grand scheme of the total cost of redoing a road is it really that much more."
Well exactly. Makes you wonder about 'accounting methods'.
Of course inconvenience and danger only make it onto the 'balance sheet' in extreme circumstances - even then it will be someone else's balance sheet...
Poor surfaces (etc.) put people off cycling, so there are more vehicle trips which wear out the road quicker...
Especially at junctions where vehicles have to cross cycle lanes and are usually accelerating so likely to wear out that section faster!