Steve, I've been looking into this for some time now and haven't found anything yet that would make your suggestion in doubt...
The device I have for scanning OBDII is good and lets me see some limited "live" data on my MB. Its very handy once you understand what the system is doing. Having said that, the real knowledge, as you know, is in the data stream both to and from the PCM... especially in the 96 and later cars.
Still not sure what the Snap-On can see beyond the engine/trans, but that's enough for me at this point. The data available will be several orders of magnitude better than I had previously and will help pinpoint not just the "what" but also the "why".
I managed to get a used head unit for just over 200 dollars off eBay, so even if I buy a new MB module from Snap-On, I'll be in the 800 buck category. Not bad. Also, the cabling that comes with the MB module is already set up for the 38 pin connector... just plug it in and turn it on.
For what its worth, I appreciate your original suggestion and your taking the time to point out the MT2500 as an option to learn more about these cars.
I'm still curious about what other systems, if any, it can scan, but those will be a bonus.
Regards,

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KenP

1996 S500 W140 Coupe