I spend thousands every year for data systems alone, never mind books. This includes $2800 a year for MB WIS (Workshop Information System) alone. From my experience about half to 75% of what I have available on your car is available on the CD-Rom.
The CD covers Chassis manual, Electrical Troubleshooting Manual, Engine Manuals, Maintenance Manual, Owners manual, and Climate Control Manual. The other things I use are the Diagnostic Manuals (probably around $1-1.5k), service bulletins and diagnostic directory, New product manuals and parts info.
I have all the Chassis CD's but I use them seldomly as I also have the print manuals. I have heard many people claim that all the manuals aren't there, but I have found everything that I ever thought should be there. It's really hard to "flip" through the manual as one would with paper. I am very familiar with where things are in the manuals so I don't find the CDs that difficult. I presume they could be difficult without knowing the MB group system.
Bosch Master, ASE Master, L1
33 years MB technician