Succubus is known for it's "Lesser Invisibility" so Stealth shouldn't be out of line and the main problem right now with it is that as a 4/3 with no innate protection it's very easily traded with 3/2 2-drops and the like.
3/3 means it still has some decent power, and, unlike Jungle Panther for example, is not easily vulnerable to the cheaper AoE effects. While it would still trade with 3/2's and the like, it would have a much better chance of doing some other work before then, and still do well against 2/3's.
Thoughts? Comments? Questions?