For landscapes, unless you shoot in bad weather, I'd say the weight, battery life (overall portability) and pixel count easily goes to the 5D2. For BIF, the focus system on the 1Ds2 will hold the distinct advantage--unless you learn to use only the center focusing point on the 5D2.
When I was investigating this same upgrade scenario a month or so ago, I ended up with the 1Ds2 and couldn't be happier! I spent considerably less on the camera body (I would have had to add the expensive grip to the 5D2 since I shoot portraits), and have used the money on extra lenses.
I'm not so sure there is a "wrong" decision here. If you got a nice used 1Ds2 for around $2,200 and found that you didn't like it, you could easily resell it for the same price. In the end, if you haven't handled a 1-series, I would encourage you to give it a try. There are so many intangibles that are hard to describe with Canon's top of the line series.