Even knowing looks are subjective, I'll throw in my 2 cents and say I think the 05's look sweet. I like the box look. The inside is nicer too, and more functional. I love the back cargo area, and the inside seems more roomy. I'm a little over 6' and about 300lbs so I notice when the space is too small.
My only real complaint with the interior is that they made the roof a little different. It "feels" lower but when actually comparing to our 2000 model I guess it is about the same.
And the power, oh my gosh, it actually has some this time around. Our 2000 SE model is a gutless wonder and the new 05 just confirms what we've been missing. Sadly, the only improvements the older X's had was the supercharger, which I understand really wasn't all that either. The power is very comparable to my 02 Chevy truck with the 5.3V8 that I recently sold. Granted, the V8 had a little more, but it was close.
Can't comment much on the offroadability of either model. I took the 2000 out once and was telling a buddy how I was teter-tottering on a ledge, and the wife heard....well, I haven't been able to take it out like that since. But it's okay, I just bought a Jeep Wrangler and it has more than enough offroad capability. If you want to get crazy, get a Jeep. If you want to have some fun and haul stuff get the Xterra. I'd get the 05 simply for the bigger engine. I am beginning to hate the 00 gutless wonder.