Well we are a family of four and I can assure you when we did have a mutuelle we spent 1200 and recovered 200ish. Yes it is insurance, you would expect to pay out more than you recover most years, I don't think I have ever made a car claim, and this year (cambriolé) was the first house claim I have made for ages, I expect to lose money. Insurance is to make sure that in the event of a true disaster you aren't bankrupted, like the house burning down for example. This doesn't happen as a result of the good French health system, and as such a mutuelle is not essential.
As for specs I get them from UK by internet, my specs prescription is about as complex as is possible, they cost erm, under £200, as opposed to 750€ here. Mutuelle schmutuelle.
I do get Valerie's point below about budgetting, but I still think it would be better to put 1000€ in an emergency fund, rather than pay 1000 every year which you'll never get back.