Hi Brian,
First of all I'm not in a hurry but 7 months is time enough to start worrying if you get no response at all to any emails after at least 4 months of silence (I didn't say anything 'till then)...so I did not make any pressure at all to Mike untill now.
He could be making Lotus parts out of love of the marquee as you say, but he gets paid for that (full pay in advance before even thinking starting the job) and if he has so many jobs, either don't take them or make a real bussiness with that (taking more people to help, etc...).
He could also ask for the payment once he can start the job...that could be as well a solution, so people don't get ungry waiting for too long for the parts.
I also think he should stay on this bussiness (I've been looking for a pair of mirrors for my S2 since I bought the car and Mike is the only one who gave me a solution), but call it as it is and do it properly. As you say, he can be really good and will be a big loss to lose his services, but you can lose it yourself if you don't do it properly...that's all.
Maybe is just a problem of comunication...you see, I'm getting nervous because after 7 months I have no idea of what's up with my mirrors, and now it seems like they are done and on the way home...
...or maybe not?