I took both out this time round...
There are two types of GAP insurance and the amounts paid out reflect in the purchase cost.
Return to Invoice and new car I think they are classed as..
I took tyre and rim insurance out at about £299, I'd not had it before and only ever once caught a rim- although lost a few tyres due to pot holes etc..
I noticed that the rears had very little tyre protection so I took it out.
Following the trip to Monaco and the Eurotunnel I discovered that I can't get on the standard carriage without catching a rim by as I pass the toilet blocks
This resulted in two rims getting damaged, pleased to say that the repairs were done to an excellent standard and paid for via the insurance. At £100 per rim I'm almost ahead!!
GAP insurance, pleased to say I've never had to claim on it... although many will point out that for a new car your own insurance will usually cover a full replacement for the first year.
I see it as year 2 and 3 that if the worse happens, then its a winner.