DavvaP,
No I would not say you're "far too dumb".... yours are valid questions.
You're right, "it would have been too big an undertaking for too little benefit".
Don't forget the history... it was the governments that financed development, manufacture and (initially) operations.
By the time the last few aircraft came off the production line they were already unsaleable 'white tails'.
Now, the "B" modifications to the wing were quite major (droop leading edge, extended wingtip, other tweaks) and to reftrofit them would have been difficult and costly.
The "B" engine had a larger frontal diameter, so the engine nacelles would have had to be redesigned and re-manufactured.
All those modifications would then have to have been revalidated and recertified, then applied to each of the aircraft, plus the manufacture of new spares, etc.
Still saddled with five unsold aircraft at the time, there was no way the governments were going to finance such a major upgrade.
As to G-BOAG...
Applying some or all of the modifications to G-BOAG only would have been pure folly, because it would have meant a large separate spares store, revalidation and recertification, separate documentation, etc. etc. all for one aircraft.
Finally, the story doesn't tell if Rolls Royce ever got as far as running a prototype "B" type engine on a test bed. Certainly, none were ever manufactured.
CJ