I await Big Rods comments on here... 
OK here goes...............
A 12v C30NE Senator is pretty much indestructable as opposed to the 24v C30SE but at the sacrifice of 30 odd BHP.
I'm inclined to agree that the chains debate is a bit of a storm in a teacup. However this was an issue that Vx recognised and recalled a lot of them to have the chains replaced. These should have a 'blue spot' somewhere around the Dual Ram servo on the induction piping. But can you be guaranteed that it's been done and not just some greedy dealer 'dotting' it and claiming the warranty work? Upgraded, (F1 spec), chains and replacement guides are available through the Autobahnstormers.
One thing I do know goes the way of the pear is the CHG at some point after 100k miles. The gasket between the oil channels and the outside world leaks down the off side of the engine block. It's sometimes misdiagnosed as a sump leak. It's best to get it fixed there and then before the coolant and oil start mixing. If they do, you can say goodbye to your bottom end after about 2k miles.
Once you procure your Senator, if you want to keep it, the parts alone to do the CHG and chains properly will set you back about £700. If you can do the job yourself, (I did once and it is by no means impossible!!). Fit an ABS chip, remove the cat's, skim the head/block, fit a widened throttle body , do a bit of porting and match the induction ports while the head's off and fit a K&N filter then you should realise about 240 (conservative estimate!) BHP.
There are other issues like the one's with the dizzy that Mark pointed out and the oil cooler thermostat have a regular habit of failing, but is never noticed until the car is thrashed.
Finding one with working aircon is difficult but not ultimately impossible.
If you're looking for reliability, find a very late 3.0 12v model they have better fueling systems and have bigger valve heads to compensate for cats. If you want power, get a 24v, but they need looking after.
All ecu upgrades and many parts are available through the Autobahnstormers.
And if you need any spares, I've got loads!!
And if you want to know anything else, let me know, I'm happy to help.