Had the same problem with my '98 E320. Had it towed on two occasions because of the no-start condition and because I had the extended warranty.
The first time, they placed fault with the infrared key and replaced it. I'm not sure if the ignition switch was changed as well, but all was well. Like you, when the MBenz tech came out, he diagnosed a bad battery and replaced it (had to pay for the battery - but it was about due anyway).
The second time, it tried to start, but wouldn't. The starter would crank but it was as if there was no fuel. So I made another call to roadside assistance. Before they could get to where I was located, and after about 15 minutes, it started on its own and ran fine for the next few weeks.
The third time it happened, I had the car towed and this time they replaced the crankshaft position sensor.
About a month after that I sold the car, glad to be rid of it. Although I am a loyal MB owner and will buy another E320 soon (it will be a '97 without the infrared key and with the old inline 6 engine), I had had enough. That car was about as unreliable as my two Jaguars (ouch).
I don't know if this helps, but rest assured, you are not alone!
300SD ('81), 190E ('89), 420SEL ('86?), Jaguar XJ6 VDP ('96), E320 ('95), Jaguar XJ6 ('97), E320 [S210] 4matic wagon ('98), Nissan Maxima SE ('02), DeVille ('93), BMW 325 ('03), LS430 Ultra ('01), Avalon Limited ('05), S430 ('06), MINI Cooper ('05), Toyota Camry ('07), Hyundai Azera Limited ('07), E350 ('06), LS430 ('05)
Nissan Versa ('08), S430 ('03)