I do believe that as the weather warms up the new park will be less pitcher friendly, but I also believe it will never be close to neutral either.
You'd think so, but the weather doesn't really change much in San Diego, kind of a year round low 80's type thing.
I did some research on this subject for the sake of accurate projections and I found out that during the spring the air is heavier by the ocean at night, but once summer comes around the air thins out. Since their new park is right on the water (the bay, I think)there is some thought that that is a big reason for the lack of HR's there so far. I'm no meteoroligist, but this was a good enough reason for me not to jump into any hasty conclusions just yet. Still, it's a mighty big park.