Ok, some facts.
DPF is only fitted to Zafira and Astra Twin top - Not an issue if you follow the instructions in the user manual when it regens!
16V - These are the 150bhp ones, the 8V is 120bhp. The 16V has the oil filler on the right side of the cover, the 8V is on the left (easiest wat to ID them). There was a short period where 16V units were fitted to 120bhp models and the MAP modified to lower the output due to a shortage in 8V pwoer plants.
EGR's can stick (seems all to common on diesels of all makes sadly these days mine has stuck once in 40K miles). These are VERY easy to remove and clean and I am yet to have to replace one.
The Vectra uses the F40 gearbox which is stronger than the Astra/Zafira M32 unit so no worries here. The M32 generally only suffers issues if you up the power to 200bhp with a tuning box or re-map.
If looking at one, start it up 5 times and listen for a clack when it fires, this can be a sign of the DMF getting loose (again, all to common on modern cars ranging from VAG to Ford etc etc). Agaian, its not as common as some make out.
All in, not a bad engine.
The 16V unit has swirl flaps (the 8V does not) pre 2007 cars can ahev issues with these sticking, a modified inlet was fitted after this (and retro fitted to units with issues) which resolved this fault.