Keep your standalone if you like, me I prefer to be able to link my 3d data (f-curves or any thing else for that matter) to my compostitor to control things like DOF among zillions of other things. Or I can use the compositor to do things to my textures without having to render the images out, in fact I can see my results happen in real time in either open GL or Mental Ray.
XSI compositor is missing a few things for sure, but it is built on a far better core than AE or Combustion thats for sure and the intergration is to die for. And I dont think you can compare AE scripting to XSI's.