It's a very nice car, no doubt, but unless you're doing virtually no miles is it really worth the extra running costs?
An Omega can get through a bit of fuel, but that will be in a different league, especially if driven hard. I don't know about you, but it's not that often I use everything the Omega has to give and want for more. Are you ever going to use all those horses?
Granted there are times when you can't have too much power, but you pay for having extra power every mile you drive. With fuel costs increasing with no end in sight at the moment, it just feels like the wrong time to buy something more thirsty.
If you want a more nippy car (let's face it, no-one needs to better the top end performance of a V6 Omega in the UK), go for something lighter and less thirsty. Keep the Omega as a cruising barge.
On the other hand, if that car is affordable to run now, it sure as hell won't be in a few years time, so if it's something you've always wanted, go for it now.
Kevin