I had a 4.2 convertible for two years and didn't need the wind shield. Baased upon this car, a neighbours 5.0 convertible and a previous generation XK8 I owned I'd say the weak points are the electrics, but all issues were covered by warranty.
On my XK8 the drivers seat failed. Don't know exactly what my neighbours issues were but I know it went back a few times for the same issue. I've had a memory failure on the detail for my XK!
Most electrical gremlins are usually down to the battery getting tired, especially on cars that don't get used much. It's well documented with a Google search. Get a good battery + battery conditioner and you'll be fine.
The wind deflector makes a massive difference and is well worth having. It's very expensive though for what is basically a bit of bent alloy tube and mesh.
Some decent aftermarket companies make them for half the price, may be worth a look.
