I have looked into changing the rear tail lights to the 98-00, but each side is roughly $200. Not worth it, unless they somehow get damaged. THen I would do it.

As for the headlight lens, I believe those are a little cheaper. Something like $125 (don't quote me). I think you can get the 98-00 ones at bekker.com. I have also thought about doing this. But probably will not until/if it needs to be done.
As for the HID, you're looking at $1700 + to get OEM ones, DEFINITLY not worth it.

The turn signals (clear corners) can be had for a lot cheaper (I think about $50 or so). You can try www.bekkers.com for them, I think they have them There was also a recent post in the OPEN DISCUSSION on this (probably on 2nd page now). Try looking there.

Good luck!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)