I’ve not really used the NewBlue bundle yet – not because I don’t thibnk it’s any good, but because I’ve been doing “boring” corporate stuff. Similarly, I’ve been perfectly happy with the built in Satbilisation – but that’s because 90%+ of my footage is shot on a tripod, so there’s not a lot of post-stabilisation needed.
Your best bang for buck is to go for an decent nVidia GeForce card. I know Sony and all the “pro” system builders’ll recommend Quadro cards but for mine they’re (a) expensive and (b) based on old technology. For decent GPU assist, you need two things – lots of CUDA cores and plenty of GPU memory bandwidth. I currently use a (slightly) overclocked GTX570 card and it’s rock solid and blazingly fast. These days, a GTX670 would be the way to go. It’s based on nVidia’s latest Kepler core, and has 256bits of memory bandwidth, which is as good as you’re likely to get. Try not to go lower (66Ti , for example) because their memory bandwidth is constrained to 192 bits, and that’ll hurt performance. And stay away from ATI/AMD cards – there’s nothing wrong with them per se, but Vegas is optimised for nVidia’s CUDA architecture at the moment.
The second best bang for your buck is memory – I run 16G, and will soon be bumping that to 32G. You can never have too much memory 🙂