Reviewers seem to feel that the Ghibli really comes alive with the S Q4. If driving enjoyment is important to you, and if you value some of the extra features that come with the S Q4, it really is the best choice.
IMO the S Q4 is a no brainier. Better engine, AWD, sun roof, navigation, Bluetooth, rain sensor, alone is more than worth the money and I have not included the entire list of differences. Look at the pricing list for all the differences. The AWD is rear wheel dependant especially from a standstill which is a must for enthusiasts. Like I said no brainier for 10k.
If you're going to purchase a Ghibli, why would you not opt for the S Q4? If money is the issue, stop looking at it and buy a more affordable car. I mean that in a sensible advice way. Otherwise, given the performance and options differences the choice obvious. Seriously, that car shouldn't leave the factory with less than a $80k MSRP after options, just wouldn't be proper.