I have a whole thread over at CGTalk in the Vue forum comparing Vue and Carrara - if you really want an ALL AROUND (by that I mean landscapes & environments) then IMO, I don't think you'll get better than Carrara right at the moment.
XSI while powerful and "sexy" as I like to say, has no landscaping capabilities at all, neither does most of the "power apps". Vue to me has always been to slow and "dis-promising"; the things that they promise you can do either you can't because of bugs or it takes a lifetime for it to render...
Maxon is currently having a sale for Cinema 4D:
http://maxon.net/pages/dyn_files/dyn...315_02315.html
I'm assuming that sharbor will honor that sale with even better pricing...
Again, C4D is about the closest you'll get to Carrara "feel" wise, including landscapes and environments (it has skies if you get the advanced renderer module and terrains/water are a breeze to do in C4D.)
-Will