Mike, I agree about the (unfortunately) over-optimistic aspects of flying a BRITISH aircraft circa 2012, but these are not particularly huge avionics issues. (I would hope that no person in their right mind would suggest a wholesale avionics upgrade for such a venture/dream, no one). There would of course be a cost, in terms of an avionics systems review and complete test and calibration, but apart from the possible worry about power contactor condition, the rest of the airplane should 'fire up' without too much of a problem. Provided certain pieces of test equipment could be obtained, this should not present TOO much of a headache. (Fortunately there is still quite a wealth of expertise around, on both sides of the English Channel).
The REAL problem, as far as a British aircraft is concerned, is a simple one of fluids, namely hydraulics. With hydraulic oil being drained from the Green, Blue and Yellow systems when the aircraft were retired, the systems' seals will likely to have deteriorated, and possibly dried, and maybe even shrunk/cracked. (Although the Viton GLT hydraulic seals that were retro-fitted to the aircraft in the 1980's/90's were a huge improvement over the original fit, in terms of aging deterioration, and proved to be quite resilient in service).
An even bigger issue is that Chevron M2V fluid is extremely sensitive to water contamination; I seem to remember the limit being in the order of 8ppm, and only a small increase above this would render all components useless, due to contamination. So you are faced with the potential cost of a complete systems strip-down and component overhaul, and even if this WERE financially viable, time is not on our side here, in terms of 2012.
We therefore unfortunately have to take a firm grip on reality, in terms of what is possible and what is not. As much as most of us in the Concorde 'family' would love to see an aircraft fly this side of the Channel, it is not really feasible I'm afraid, at least in the immediate future.
(But it costs nothing at all to dream
).