I think you've listed the weak points.
My subjective opinion is that wiring harness problems happen on 400E's, by not nearly as common as failures on 1993-1995 300E (3.2's and 2.8's) and E320's. I think the failure rate on 400E's might be more likely on '92-'93's than the later '94-'95 E420's. I'm sure you also know that '92 and '93 400E's have the same 4.2 liter engine as '94-'95 E420's. Mercedes gets the badging wrong sometimes. It's the same on the 1993 300 TE, which has the same 3.2 liter M104 engine as '94 - '95 E320 wagons. They just didn't change the badge in 1993 as they should have.
Also, after reading thousands of posts, the failure rate on evaporators on post 1989 W124's is very low. The failure rate on the earlier ones was much higher. You'll still have the failure of the vacuum operated valves inside the dash, though.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".