Whatever you choose is the right decision. We all have different impressions of cars, we all have different uses for cars. Is it a daily, a highway machine, groceries, posers car etc...
Number of seats?
IMO this is what I think of the cars mentioned.
R8: Decent value for money considering what it is. But buy it because you love the car, not because you think it is a more economical version of a Gallardo (some people buy them because on paper they are similar to a G and use some of the same components). Having driven the V8 and the V10 they still don't compare to a Gallardo. Basically the car is good on it's own merrits but don't go comparing it to Lambo. Also it looks like a swollen Audi TT.
DB9: To me they look out dated. Years ago I thought they were the nicest looking car but today I look at them and they look out dated and pretty mild. But this comes down to you and your personal preference. No idea what they are like to drive but I've driven the Vanquish(2004 model) and V8 Vantage and they were both great easy cars to drive. I'm sure the DB9 is just as good or even better.
XKR: Well it is a new car, Classy, sporty, IMO the nicest looking (probably the nicest looking car today). I think the XKR looks more classy than the DB9 and more sporty and agressive at the same time.
If this was my decision I would definately go the Jag, and being a new car you get the factory warranty as a bonus.
Don't know what you want the car for but 430's and +06 model Gallardos are now starting to get into your price range incase you haven't looked into them too much.
Cheers and Goodluck