The reason the weather is so slow in the screenies is because I put a delay on it. I just tested both the rain and snow without the delay, and it's much better speed-wise, and it still looks good. I put the delay in for testing purposes, because I wanted to make sure nothing corrupted or went wrong. I'll look for some tilemapper-related optimizations as well.
I'm thinking that perhaps certain shops will only be open during the day, and others during the night. Or maybe at night you'll be able to sneak into certain places because the guards will be sleeping at their post. The different enemies appearing at night is an idea, or perhaps they'll just appear more often or in more places.