I believe that if you wait until Output releases their next product (they usually do one a year, but last year there were two), you will be able to get everything in the NI deal plus even more expansions than have been released as of today. For not much more money.
Sometimes the NI NKS sales are insanely good--for example, Orchestra Tools. This is not, in my opinion, a good deal at all for an Output package. Depending on who you are, you may lose money on it. There is no reason to buy it unless you only want something like Signal (best price so far) and are sure you want nothing more, including the expansions, which cost $35, I've never seen discounted, and really take their instruments to a new level.
If you like any Output instrument, you're probably going to like all of them, because each one has a very similar user interface. That's part of what is good about them--after you learn one, there's very little learning curve on getting the most out of libraries that have very different sounds.
Think about it this way: if you buy every Native Instruments or IK or Soundtoys or Output product as they are released, you will spend a LOT more than you need to. All of those companies offer an INSANE deal if you buy everything they've got--and often there are sales on that. Of all of the companies I know, Output is by far most generous in supporting their best customers. It's not just because they an amazing deal at the first point of purchase--they give you amazing deals every time they come out with something. The new product at a discounted rate and all the expansions that have been released in the interim.
That said, if people only want Signal, they should just get Signal.