Weirdly, I also bought an '03 Targa from Wimbledon Carriage Co. - but almost 2 years ago. I took the full 3 year AutoProtect warranty for £900 as it seemed like peace of mind. But before signing on the dotted line I had the car inspected independently and checked and double-checked that the policy would cover any IMS issues or any other major mechanical failure - which they assured me it would.
That said, I've never had to use it yet as the car has been ultra-reliable and nothing has been needed beyond servicing, so I guess we'll see. One year still remaining on the warranty.
I'd be very interested to know more details about your car and what you paid for it. Also, since purchase I've been using WCC for servicing and they seem quite good, if a little pricey. They know the car well and are always very attentive. Would be good to hear your opinion - Do you live locally?
Cheers
Paul