I threw an intake vanos code last week and felt at 69K, my mods, and what ive heard about the solenoids it would be good practice to replace both. (especially since they are relatively inexpensive compared (210 total) compared to other things ive had to replace...
This work is EASY. It was even more convenient I was putting my Procede back in so the cowl had to come off anyways.
DEFINITELY good practice to replace one at a time, I did the bottom first, then top. Barely any oil dripped out.
NOTE: I have an 07 335i N54 and it was definitely NOT necessary to remove the snorkel. PLENTY of room to get the bolts/parts out with an 8mm long socket and a 3/8 wrench, and my hands are not small!