Mr Potential,
I wouldn't consider the Reliant Scimitar comparable with a Bristol. Not that there is anything wrong with Scimitar, but it's a very different car. To be honest nothing is quite like a Bristol!
The Mercedes 450 SLC has certainly stood the test of time. Probably has better build quality than a V8 Bristol. But it's much smaller than a V8 Bristol and I can't imagine it would carry four adults in the same comfort as a Bristol. Cons: Common as muck, ex pimp car.
I quite like the Rover and have toyed with the idea of buying one myself, but I would want a P5B Coupe. I don't believe they had any build quality issues. It was good enough for the Prime Minister!
Lancia Flavia coupe is a great looking car, but I don't know much about it.
Other suggestions,
BMW 2800 CS
Bentley T1
Jaguar XJ6 Coupe
There was a time you could have got a good Gordon Keeble for that money, or an Aston DBS, but not any more...
With the V8 Bristol you are paying for exclusivity and a bit of mystique. Having helped pull one apart, I personally don't think the engineering or build quality is superior to most of the other cars here. You can definitely tell they were hand made. But, if you start with a good one it would be one of the easiest to maintain.