The 3.2 is no heavier than the 2.5/2.6/3.0

Serviced they will easily run to 275k miles and beyond. But it's an Omega so all the usual Omega things apply as they happen to all of them:
1. Heater bypass valves fail dumping coolant everywhere. Cheap and easy to fix but usually misdiagnosed as a much bigger issue.
2. Suspension bushes wear and fail. Budget £800 to rebuild the suspension properly, more if you need tyres and can't twirl a spanner.
3. Crank sensors fail and reliable replacements are getting harder to find.
4. Misfires. Usually water related causing coil pack failure and rough running.
5. Cambelt failures caused by neglect or not changing the pullies with the belt. 40k/4 years is the official interval.
6. Oil cooler failure caused by poor coolant maintenance/incorrect coolant.
7. Central locking motors fail and front door latches start to bind and eventually seize. Especially the drivers one.
8. It's 21 years old. So expect the potential for significant rust on the front chassis, rear sills and arches. Also the bulkhead area if the scuttle hasn't been kept clean.
A nice, well kept car should be worth a a few thousand, but a neglected shed might be really cheap, but expect to throw a couple of grand at it before the next MoT.
Check the MoT history.