I have some buddies in the motor trade and they tell me that a 'full dealer service history' adds no significant value to a car at all. While in the first year or 2 there may be an argument to do it for warranties (and that's not even a legal requirement in the UK any longer)
Test it when you ask for a trade in value. At most they will ask if recently serviced. For a private sale it can give comfort to a potential buyer however a pile of receipts for work done, spares, etc. is of equal value.
in the latter years the massive extra cost of dealer service far outweights any incremental sale value. I recently had a level 3 service done on my X5. Dealer was asking £650. Local guy did it for £200, car collected, valeted and returned. Is my X now worth £450 less, or if I went to BMW to trade would I get book plus £450