I'm very happy with my Biturbo and I don't 'need' another four door classic taking up space, but I'd still love a QPIV some day - what's it actually like to own and drive Ewan...?
In a word, quirky! It's hard to sensibly justify it over an equivalent era 5 series BMW or Jag, but way more interesting and stylish. And it's strangely satisfying to know you are driving a little piece of Italian vehicular history.
The driving position is a little unusual, and not best suited to all body shapes. But overall it's a comfy enough place to while away a journey. Quick too - in period (circa 1996) it was the fastest 4 door car you could buy.
Ownership is fine, as long as you have someone that knows these cars. Certainly a better proposition than a 3200 from the same era, with better parts availability (strangely).
I'm lucky as Emblem is close to me, and the key Maserati mechanic there (Myles) is the chap that PDI'd my car when it was first imported back in 1997. So he's worked on it since new.
Engine-wise, best to go for the V8 version, as if you are buying a left-field choice car, you may as well go top-of-the-range. Also, you've had a V6 in your biturbo, so if you were to change/add, you may as well step-up.
Manual v Auto is a matter of personal preference. Both boxes are fine.
All that said, they are not the most robust vehicles ever, and there are not many available, so as is probably stating the obvious, it's sensible to concentrate on condition over spec/mileage/colour etc. They are 25 years old now, so rust is something to watch for.
£10k should get you an okay example. £15k a really good one. £20k the very best one.