The 2.4 diesel is great engine in terms of performance. I don't know from experience but I gather it is different then in the 156. Particularly adding a DPF which are a nightmare. From personal experience don't get a diesel if you do low miles. I know that is a general rule of thumb anyway, but with past cars I have ignored it with no problem. However, this one seems to clogg easy which is proving expensive to recitify.
That being said, unless your budget can stretch to one with the 1.75 200bhp+ turbo petrol, then the 2.4 is the most powerful you can get outside of the V6. Don't think it's econmical either, because it's not.
I do love the 2.4 when running sweet... but I sometimes wish that I had brought a 2.2 petrol with a remap. Hopefully come next week and over £1000 later I'll be glad I had the 2.4jtdm again!
Oh and if your budget doesn't strech to TI then a Lusso with 18's and lowering springs looks just as good.