There are cards for the DS that sit relatively flush to the system. The buttons and Dpad do feel noticeably different to me, and I prefer my DS Lite much more.
As for hackability, they are the same. Both can use passme devices and both can be flashed. You need the newest flashme for the DS Lite, but you should be using that anyway. Both are easy to flash and work just fine.
The DS Lite screen is worth the extra cost BY FAR. It is so much nicer, its like a completely different system. I like the look of the lite, and the smaller form factor, but the screens are worth it more than anything else.