They are just like night and day. Here are a few:
-Better LCD in Z1
Not really, just bigger
And bigger is BETTER. Any girl who tells you different it just trying to make you fill better about your small "inadequacy". 
-Faster NAV in Z1 thanks for the built-in HDD
Only slightly. We're talking about maybe a second or so faster calculating routes
A second is all that might stand between you and Taco Bell! I'll take every second I can get.
See comment #1
-10GB to store your music
Don't need that
Personally I love this feature. If all you have are MP3's you ripped from somewhere, not a big deal. Or if you have a lot of music published in the last 5 months. But if you have a large CD collection, it's nice having a voice searchable music selection with no input into the thing at all. Just 50 or so of my favorite CD's (all I put in there so far).
-Bluetooth in Z1
Have you read any of the posts about how "great" the pioneer bt interface is?
There is a fix from pioneer (reported). If it's really true it will come out sooner or later. As it is, it's usable, not the best, but usable.
-Voice command in Z1
Useless if you have any kind of accent or drive with the windows down.
Yes, you can't sound like Borat or have the windows open. But if you have a decently quiet car, I think it picks up stuff rather well. Not perfect, but it picks up my songs from my library pretty well. The nav controls are a little more difficult, but not too bad.
-Made in Japan for Z1
And this means what? So is almost every other piece of pioneer equipment
"What are you talkin' about, Doc? All the best stuff's made in Japan..." (BTTF, Michael J Fox)
-Play DVD video in Z1
Yeah that doesn't bother me. That's why there's a ps2 in my glove box. Now I can play videogames too.
Yah, but you can control the DVD right from the controls on the screen, great for my daughter who is in the back and is only 3. So I have a movie controlled by me but she watches the screen on the rear monitor. I think that set up is much nicer than having an external DVD player (even if it is a PS2. But I would love to play GTA3 while actually doing GTA3 things in real life!
That's my take on the benefits of the z1. Me I'm perfectly happy with my d1 and all of it's little quirks.
There is nothing wrong with the d1 or the d2 for that matter. But I personally like the new features in the Z1. But that's just me.