Very unfortunate circumstances. Your next technician will really be working under the gun, with you having already spent at least enough to fix the problem.
I agree that a Bosch Service Center will have the proper tooling to analyze your situation. (that doesn't mean they will use their heads, though, unfortunately). Ultimately your fuel system requires some form of differential flow meter or a lot of experience to diagnose without the parts replacement method currently being used.
I would normally say to stay with the first technician as it is his failure and one shouldn't have to pay for retesting which obviously needs to be done. I don't think from the sweeping proposals (needs plug wires) that real diagnostics are taking place. I have replaced a few sets of plug wires in 27 years but only because the sum total of individual failures and overall condition suggested it. If you have a plug wire failure (or two or whatever) they are easily viewed using secondary ignition scopes.
Your worse case senario is a bad fuel distributor. You need to start with someone that can make such a diagnosis, confidently. (with testing back-up).
Bosch Master, ASE Master, L1
33 years MB technician