I've just seen this thread by fluke after looking at the piccies for the Factory visit (which look great btw). I've got to say how shocked I am and deeply sorry that you've got this problem. I feel guilty as although everyone experiences various probs with the Esprit, you're still in the honeymoon period and should not be having this grief.
As you're aware the car was maintained to a high level and of course had various bits done on her that gave the performance that others have talked about. That said, as you know increased performance does result in decreased reliability.
Hopefully this may help/explain some of what you've seen.
The spark plugs were originally NGK I recall, but decided to change them for Iridium ones. Remembering now I had a very (and I mean most people would never notice) minor misfire under load at speed in 5th (about 90), I was flumoxed (!) about what it was, checked the leads, realised that they'd been attached incorrectly at the coil (something Jon refers to) and re-connected them thinking this MUST be the problem. This was last year I think (it maybe early this year). It wasn't the problem so I looked further. I noticed that a couple of plugs were showing signs of running hot so I ordered a pack of lower temp ones and replaced them on C1 and C2 I think, this cured the misfire under load so after testing I left them in. I think in all confusion I probably left the original ones in - but was happy with curing the fault so went on to something else. Apologies if this has caused a problem, but at least you know the reason behind it. Not sure why the original plugs were hot or breaking down but assumed this may be because of some other change (like the de-cat/chipping etc.).Things were back to normal.
wrt the boost control not working - well that's a new one on me. I know it did work perfectly (you will have noticed reduced boost too when the engine was cold). We both spoke about this on the test drive that it gets restricted to .25bar until warmed up (about 60c I think) and then will let full boost through. If this was failing you would have seen the check engine light as the ECU would have seen wrong inputs from its sensors. Could this be something else you mean ?
There was an issue with one of the vaccuum control pipes a month or two before it was sold. I was in the car in Manchester and she developed a very bad lurching /poor engine control. The car was limped down to the local Lotus dealer who put their scanner on to find out what the problem was - lots of head scratching and 3 hours later the problem was found - a decayed rubber pipe that has split and was letting in air. They replaced the pipe and believe it or not didn't charge me for the pipe OR labour !! I was well chuffed. Hence why no invoice in the pack of paper I gave you - it was also so blimen simple that I was annoyed. On the way home the pipe blew off where they hadn't attached the new one properly but knowing now where it was (in the middle to the right of the turbo as you look at the car from the rear) I plugged it back on properly and was away. This is the typically silly things that Lotus owners get annoyed about (just like the turbo wastegate split pin I told you about).
wrt being beaten off the lights by a Ford Focus - well shall we say that would never have happened in my day ;-) I think there turbo comes in about 1900rpm so will get the jump on a GT3 until the turbo starts spinning, that may be a whole second later, that's a fair bit of ground until you catch up. Power, weight and all that.
To be honest and knowing how close this group is, if there were any known faults the car wouldn't have been sold until they were rectified. I am so terribly shocked and sorry that she's off the road - I only hope that you can get her fixed and back giving you some joy asap. If you want to talk to me, please ring and I'll be as helpful as I can - I want the best for any Esprit and of course you matey.
btw I liked your wing mirrors, not sure about changing the spoiler imho (I searched for your threads). Were you serious about replacing the engine for an Audi one ?