True, though I consider them a 'modern classic'. Certainly she does get the odd admiring looks, and had a few people come over and ask about her, engine size etc. I think any car which people actually have positive memories of has to be a good thing, and some form of merit/classic status. However, as you say, 'classic' is a loaded word and it is used for anything over, say, 25 years old.
Give it a few more years when they're doing 'retro' Police Dramas (same way Ashes to Ashes/Life on Mars did a few years ago now) and there's CID/unmarked Police Omegas everywhere, then people will start to remember/reminisce. there was plenty of groups of people who had fond memories of them...
-Royal Family ran them, Prince Charles in particular liked them
-PM and Cabinet Ministers official transport
-As above - Police, marked and unmarked
-A thousand Managers, be it junior Manager who was able to afford a 2.0 GLS (for the same price as a Vectra you could have a base model Omega) or the bloke higher up with his Elite.
-Sounds daft, but still very popular as Hearses/limousines
-Taxi drivers there's barely a person alive who hasn't been in the back of an Omega from a night out/dinner party/ferry to the airport
Not forgetting Sir Geoffrey Norman MP had one...
https://www.youtube.com/watch?v=8946ojRoX3Y