This is fairly interesting in terms of analysis. I would say that while some of the backup information from editors might come from Wikipedia, I don't think that this is the sole reference point for much of what is said. It's not as if the additional links being provided are only Wikipedia links. In the interests of full disclosure, it should be noted here that enotes staff seek to encourage editors to not solely rely on Wikipedia as a reference point for editor work. Perhaps, there is something to be said when Wikipedia and enotes editors are so similar in their work. It might speak to the validity of the information being presented. I do think that one of the distinct advantages of enotes over Wikipedia is that editor work posted on enotes has to be approved and can be taken down by enotes staff or flagged by other editors if it does not meet specific quality standards. This level of monitoring and rectification might not be as present on such a fluid medium as Wikipedia. Another particular advantage of enotes is the ability to ask specific questions to one who has posted information. For instance, if you disagree with what I have written or cannot accept a premise I have posited, you can send a message and ask for some level of clarification. This accountability is something not as prevalent on Wikipedia. Finally, I think that the ability to access lesson plans or other items as well as other detailed elements is something that enotes affords that Wikipedia might not offer.
Those of us who answer questions on here aren't affiliated with the actual owners of the site, so this is not an official statement, but here's my take on this:
It really depends on what you are looking for. There are tons of summaries and analyses and more of so many different literary works. That is stuff you certainly cannot get on Wikipedia. There are articles about many authors that go well beyond what is on Wikipedia. The same goes for many periods in history. There are also law dictionaries and business term dictionaries and other specialized things like that.
In addition to that, you can get people to answer questions that you have. I see that you have not asked any questions yet, but depending on what your questions are, you can get good quality answers to specific questions.
Of course, you are the one to decide whether these are worth your while, but I think there is much more to this site than the links to Wikipedia.