I bought EZdrummer at full price and it was worth it even though it's about half price now a days. I feel Superior Drummer is the same but I had a different situation for that one.
Melodyne Editor is worth full price.
Reaper is worth full price but it has different licensing deals so it's not an apples to apples comparison.
Studio One is worth full price and I was prepared to do so but I got a competitive upgrade deal.
Samplitude Pro X is worth full price but once again, I found a competitive upgrade.
Although I've drifted away from SONAR, I would say that for a person who coming into the world of the DAW, SONAR is worth paying full price for.
I have Slate, Waves and UAD-2 plugs but I paid discounted prices for those. I wanted them but was willing to do without them until the deals were made available.