I think the issue here is that the OP said the bike shop contacted him about this 6 month service - Having a price list for services is fine and when he outlined the amount of work it involved you could see that in time alone it was worth it. But initially it sounded like the bike shop was taking the piss, instead of the customary free bike check they were going to charge hundreds! If the bike needs that amount of work, then voluntarily getting this done is fine, but pressurising customers who might not know much about their bikes into feeling the must do this service wether the bike needs it or not. That's the issue.
You're right about service being important, in a world of Ali Express and other direct to consumer brands, bike shops are in danger of being pushed out like independent bookshops after Amazon arrived. Service is the one area you really need a good local bike shop. I'm seeing more and more sole traders who don't bother to sell bikes just service bikes keeping overheads low. My sister needed work done on her road bike last summer on holidays in a remote-ish part of Ireland and found a young guy who operates out of van and specialises in high end road bike/MTB repairs and will come to you! He was brilliant and reasonably priced too. Clever idea.
