Yes, those old Brit bikes have a lot of allure. And of course I am biased. But let't face it, if it wasn't for modern updates (electronic ignition for one), they would still, in some cases, be the unreliable, under developed, machines that they were when new.
The only reason a Commando, for example, is a viable daily rider, is because of the immense spares backup available and the hugely enthusiastic owners clubs and forums out there. Even without either of those I would still have bought mine (because, like a lot of my generation, it was an emotional purchase driven by the lust for wanting one for many, many years) but I would not have been as comfortable about the actual day-to-day reality of ownership as I am now.
To those of you who say that you would like an old Brit bike I would say, just be patient. There are deals to be had out there, and the chances are your investment will be just that; or at least you won't lose money. However, be prepared for a completely different experience to the engineering excellence that is part of the joy of sohc ownership.