My own experience is that the cost of an extended warranty translates to a lot of work that could be done on your car, but with added headache. What's the worst that could happen? The engine blows up? That will mean a fight with the dealership and with Nissan to prove it was a defect and not something you did wrong, when you could probably just get a used 1.6L engine and have it put in your Micra for around $1000 all in with no hassles or fights if you shop around. Seriously, these are simple cars that don't require a lot of labour to fix even big problems. As such, I think you made the right choice in your decision.