Hi Mitch
I've had my 54 plate 300 SE-L since June 07 and have done about 6000 miles. A few answers and thoughts on your points:
1.) I have got between 22 and 27 mpg, mostly about 24 to 25. The display over-reads by about 10% in my case (i.e. is optimistic!). Have had over 30 showing if cruising on light throttle at up to 70mph. Once pushing it on M'ways it soon drops, but town use really guzzles the gas (presumably where the 400 excels?).
2.) I've not had noticeable lurching (and I read the very long threads) but the box does seem to drop unecessarily into 1st before reaching a standstill. I tend to ease away in any case, as befits an auto-box. IMO it's too easy to roar away and make passengers uncomfortable.
3.) No Bluetooth in mine, so can't comment.
4.) Re air suspension, I find it works fine. I quite like the lower setting on M'ways. Also you can set it to lower to allow easier entry (much welcomed by my oder relatives) so I'd have it for that alone. Obviously handy too when fully loaded as no worries about lights pointing skyward, thouh assume Xenon's would adjust anyway.
5.) The price you mention sounds about right. We paid £23k with 26,000 miles, but that was 4 months ago and they still depreciate quite quickly - though not as much as for the first owner! Make sure no corrosion on roof rails or wheels, as you can get these replaced under warranty, so worth buying just before 3yrs old, rather than just after (e.g a 2005 on 54 perhaps).
Hope that helps.
regards
Nick