I will answer some of your questions...
There is not a way to select a bunch of toys in an area...it has been talked about, but it is VERY difficult to make it happen.
As far as theming goes, there is a really nice feature where if you theme a block, then the next time you select a block and bring up the themes ribbon, you will automatically start on the last theme you used. It's a little thing, but it helps A LOT. This applies to terrain as well.
There are a TON of new setpieces, with some very cool Disney park ones that are awesome. Several have logic or special events that happen with them. That's all I will tease on that.
With the Path Creator you can build your own trains and roller coasters. We've been building stuff like that and it is pretty darn awesome. Plus new roller coaster sound effects have been made available, which adds a lot!
And lastly, the Path Creator toy has a 2D option, so you can lock the player and other things to a 2D plane! No more being forced to contain the action with Scalable Barrier Blocks.