Half-tix sell discounted tours to the Penguins, but I don't believe they actually sell discounted entry tickets to the Penguins themselves, so if you were making your own way there, you'd need to get your entry tickets at the Gate or online.
Back in "the day", Penguins plus was $10 more than general admission, and it was a great bargain. Now it's $22 more, representing almost another 100% of the general admission ticket price. I don't think that it's worth THAT much more, not in Winter at least. In Summer, when crowds are high and the place books out, it does mean you'll be seeing the penguins with a few hundred as oppposed to a few thousand others. But in Winter, that's far less of a problem.