Hi Rod,
1) The 550Ti is currently powerful enough for all I have and the overhead that LAVCUVID and madVR adds. I don't see that there will be any "harder" media you will want to play in the while I think that LAVCUVID does what it does and is unlikely to change, madVR is under constant development but who knows what (if anything) will impact the performance. FYI - I'm fine with the 550Ti - as it plays everthing I have. Note: My 1080/50p stuff is from my Camcorder so I have a bit of this (and it will grow), but many (if not most) will have none of this. If something else needs more grunt in the future, I'll just replace the card with whatever the new generation stuff is. No point it overpaying for a card now that you don't need as the price / performance ratio keeps decreasing.
2) While it seems the term GPU and VPU is generically used interchangeably, in this case it is referring to the difference between the DirectX graphics performance (GPU - eg used by TheaterView for rendering the moving icons etc), and the Video Decoding Engine (VPU - used for decoding the video streams).