I'd say weather might be nice, but a day/night system would be just as nice. I mean cmon, 2k1 had it, so it cant be -that- hard to implement. You could make it realtime, if you want, or make it so that night-time comes every say 2-4 realtime hours...
Night and day would add more roleplay element than weather, in my opinion. Like, you could roleplay reduced vision and sneaking up on people and sneaking around, or an attack of an army in the dark. Also, monsters could become stronger when it's dark, or monsters such as the HH or dungeon monsters could appear around the HH or dungeons, as if like...they're confident to emerge from their hidy-holes when it's dark
