Just going on my own insurance

100% when new
90% when a year old
80% at two years Old
70% at three years old
60% at four years old.

Should imagine their is a cut off at some point so it will never go below say 40%, I know I pay a premium to cover the extra in the event of an accident so I don't pay the depreciated value of the parts.

See below from Doha Insurance Company Policy (no not my insurers but their policy is the same), for a 2006 vehicle it would be 40% so they are letting you off lite.

http://www.dicqatar.com/DIC%20POLICY.pdf

As Hawk says, those not genuine parts may cost you nothing because they will probably cost the repairer 40% of the genuine part price and he will still claim new parts although he is only getting 70% he is making 30% in profit.

It does however depend whether you trust the fake part to be as solid as an original in an accident. It may not be structurally as well made and may crumple at the slightest touch.