Having had at a rough count 19 Omega's, the following answers are based on the experience of owning some of those vehicles on a long term basis, or only a few days/weeks.
1) When I was 18, I was looking for my first car...and initially it was going to be an Astra G 2.0 DTI. I'd always liked the look of the Omega's, but felt it wasn't the best vehicle to buy. So then I ended up with a 2.2 CDX, it had only done 28k miles when I bought it. It was excellent, never went wrong and only needed routine maintenance .It was the favoured car out of all of my friends for long distance journeys. Actually, they hated to admit it, but it was the car they always wanted to travel in. It is comfortable, quick, refined and substanially cheaper than the 5 series alternative. I could get a younger vehicle, with more equipment but with a Vauxhall badge. It never did, and still doesn't bother me it 'only' being a Vauxhall, VX have a proud heritage.
I now have x2 3.2 Manual's, both of these are preserved police vehicles, so fall outside the usual use for a vehicle.
2) No
3) I no longer have one as my every day vehicle, sadly for me they are just a bit too old, and in some circumstances I need to have a younger vehicle. My 2.6 manual Elite was replaced with a 2005/2006 Range Rover...and the equipment level really is very similiar. x4 heated seats, xenon's, cruise, sunroof, good audio, parking sensors, sat nav etc.
4) For power, yet some respectable fuel consumption...I'd suggest a 2.6 manual.
5) I prefer the look of leather, so would have that over cloth.
6) 3.2 Elite saloon
7) Capable, refined and fits in everywhere, whether that be a 5* Hotel, or the local Tesco's.

They are old vehicles now, and sadly they will and do require maintenance above and beyond what some people expect and are prepared to do. No one spends £800 on a £1000 vehicle, unless they appreciate the fact it's an Omega...not just a car.
9) No, both 3.2 manual's return better MPG than my old 2.6 Elite.
10) If you look at vehicle's circa 2003, I'd struggle to suggest much else up to £1,700 that'd be much good. The Mercedes C220 CDI 2001+ is worth a look, modern(ish) look, good mpg and well equipped if you search carefully but smaller than the Omega.