Paralysis DR is the biggest issue. You need a good CC chain to kill something, but paralysis drs with poly/hex/trap. It basically forces you to play with a target that has fear (which is tremor'd/trinket/wotf'd like crazy).
Also depends on what you're streaming. Blizzard hasn't really figured out how to use more than 2 cores, so if you're just playing WoW/SC2/etc, it's gonna be a lot less useful to bump up to SMT compared to a game that is actually parallelized.
Also, what are you upgrading from? If you're on sandy/ivy bridge, it may not even be worth spending the $$...
I'm on a laptop right now. Anything is an upgrade. My budget to build is flexible up to $1700, but I know there's a point of diminishing returns from upgrading tech when I only run 1920x1200. I'd like to be flexible on streaming anything that comes out for the next 3 years or so, when I'll look to replace again.
Why can't they just make a stacking damage buff as the game goes on starting at like 10min. Gives time for sustained damage teams to kill a target before the burst team gets +50% damage and 1 shots you.