Some people really don’t like Vectras. Well, it’s the same engine but you will never have any problem with leaking covers (aluminium ones). Cheap gaskets are ok for this one. Breathers problem? Breathers in Vectra are not going through sh... plastic cover, so there’s nothing to get blocked. Yes, after some years, nozzles might get blocked but it takes 2 minutes to clean then (don’t have to undo throttle body).
It takes bit longer to do the cam belt but nothing serious, especially that there are no trumpets to be removed. I must say that for me it’s better to adjust the cam belt.
2.5 is bit too slow, just because the flywheel is too heavy – ca 15kg, but can be skimmed and it gives a better performance. I am quite sure that Omega manual uses the same flywheel. Omega has few HP more just because longer and bigger inlet and double exhaust. You can always swap 2.5 with 3.0 engine...
Front and back suspension might be a problem so avoid vectras with tilted back wheels (like that /- -\ ).
Clutch is a pain. Most garages advice to remove the whole subframe to do it, but many can do by only pulling the gearbox.
Petrol consumption: mine is doing 39 MPG on the run (real consumption is 37.5), and 28 urban (real is 25).
This car is not as comfortable as Omega, it does not turn like omega and does not run like one, but it’s still a good and reliable. Omega for me is like a wife – gives you 20% of passion and 80% of pain and all you know that there’s something wrong but you never know what the cause. The more you try to fix it, the worse it goes...There is no passion in Vectra but there’s also no disappointment. If it’s broken, you know what it is and you’ll fix it.
It’s just my private opinion after having 3 Omegas and 3 Vectras.