Just to add my decimal pennyworth, the AF concordes were likely to have to cease flying anyway as the AVQ30 wx radar system was declared officially unsupportable in October 2003 after many months of negotiations.
Although the replacement RDR4B Honeywell system was an option, this was a small (but expensive) part of the whole economy of operating the Concorde into the future. If, as was ultimately decided, it was uneconomical to operate any longer, then it was clearly an unnecessary expense to fit the later radar as it had no use to AF outside the Concorde.
It was possible to keep the AVQ30 system going using existing unserviceable equipment and robbing parts to make good units. However, under strict JAR regulations, even this practice is now outlawed and would, at best, have added only 3 to 6 months operational life.
The BA concordes were already upgraded using the system from their B747 classics.
It's easy to forget that the cockpit analogue technology and systems were as old as the aircraft. Whilst the airframe was still very young in flying terms, the flying systems were of a different era and hellishly difficult to upgrade to comply with all the new European legislation.
Hence the astronomical costs of ownership could never be recouped within a reasonable amount of time on a pax load of 100 and a minimal cargo capacity (well, just courier mail really), no matter how much you charged for tickets.
BTW - this really is just my opinion so shoot me down in flames if it all seems b*ll***s to you knowledgeable types out there.