I have had a very similar experience with the Fidelio L1. I paid $100 for the L1 and its a great value at that price. The headphone is just so comfy, for most general listening I usually grab it now and keep the HE-500 for the serious listening. I might eventually look at the L2, but heard it was brighter than the X2 and L1 which makes it a bit more fatiguing, so the X2 would definitely be on the radar! Thanks for the impressions and comparisons!
I've never heard any of the older Fidelios, but Tyll's review, and one in Head-Fi, made me want to try the X2s. Definitely glad I did, and glad I thought to try the HM5 velours on them. Better velour, softer, and to my ears bring out more details and improve vocals without really sacrificing the bass. And they pass the sibilants/glare test. The trick is finding the best way to attach them, but it doesn't take an Einstenian imagination to come up with a few to try. The stock pads are probably a little more forgiving for less-than-ideal indie rock recordings, for example. I put the HM5 pads to the test on an album that can be downright unlistenable on some cans, and it was fine.
I'll also add that while the sound stage is smaller than the HE-500s, the imaging is better. The X2s don't approach the HE-560s in staging, but to me they're a bit more 3D than the HE-500s.