Ok, I went with the elastic suspension method and the result is simply amazing. Not a single vibration is transmitted to the case anymore, completely solving my problem with this drive. The Lian Li drive cage system wasn't able to surpress the vibrations at all but at least it's fairly well suited for using the elastic suspension method. Pics or it didn't happen:
The little rubber screw you see on the original drive sled at the top clearly wasn't up to the job.
As for the vibrations being normal or not, I really don't know. I can only compare to 2 older WD5000AAKS drives and they didn't vibrate much at all. But in the review on this site of the WD10EALS it was mentioned it vibrated quite a lot as well. Apart from the vibrations the drive is fairly quiet, it makes a light buzzing sound but inside the case it's not really noticeable.
Edit: Well, I take that back, sort of. The drive is audible inside my case as well. During the day not so much, but in the silence of the night, with the casefans at low rpm, the drive is clearly audible. Nothing unbearable, but a slight buzzing/humming sound is noticeable none the less. This is not the drive you're looking for if you want an as silent as possible system. Seems we're stuck to 5400rpm green drives for that.