vp on 1080p24 does nearly nothing.
if your projo accepts 72hz, vp will triple frame rate for judder free. but your projo mostlikely does quadriple into 120hz anyway
it may apply noise reduction. I usually turn all this off. your bd player has superb noise reduction via qdeo anyway
it may convert color space but your projo mostlikely does it ok as its not a very difficult process
it can do constant height aspect ratio if you are using 2.35:1 screen. probably you would be buying the VP for this.
color management is more precise on radiance. you are looking another 1-3% more accurate colors.
now for sd and 1080i content, i could not watch without a VP. it does nearly everything. de-interlacing, scaling, noise reduction(on cable,sat very useful I use a dedicated noise remover algolith mosquito hdmi unit just for this), aspect ratio management as most movies in sd are letterboxed your reciever will not zoom in properly.
you could get mini for 1/3 price which will do pretty much everything above(uses the same gennum chip and sw). or dvdo iscan duo. radiance xe adds analog inputs, more hdmi inputs nothing more. If you have more than 3 hdmi and analog devices(laserdisc, vhs) you would be using a radiance mini inside a xe box for 3 times to price. but then again if money is no issue,its nice to have the best of the best:)