Just get your mate to sort the problems at an agreed price between you then buy it you won't regret it, never met a MK 2 owner who has no matter how much trouble it is.
Insurance wise on my 16V, 28 with no points and 2 years NCB paid £312 with Legal and Roadside through Elephant (was also clever to get insurance end of month 29th Sept as other half paid £284 with just Legal on a 1.0 Yaris with 5 years NCB 3 days later).
chuck your wife on the Vectra as overall you'll save money.
MPG as said can be 40+ can be 15 depends on how you drive.
Look at all the parts mentioned, plus check the Pedal box as it can split and just the usual checks to a car and it's history to see how it's been looked after, serivce intervals, cambelt changes, tyre choice etc.