First of all, Wikipedia has a much larger archive then any encyclopaedia in this world. According to Wikipedia, there is 16 million articles have been saved, comparing to some proprietary encyclopaedia, Britannica for example, Britannica only got about half a million. If most of the articles are correct, larger archive always means larger amount of knowledge.
Wikipedia is as trust-able as some proprietary encyclopaedia (such as Britannica). According to a study which is done by journal Nature in 2005, they used 42 articles as the samples, based on their checking, Wikipedia got 4 errors, and Britannica got 3 errors, they concluded that the accuracy level of Wikipedia scientific articles is similar to Encyclopedia Britannica.
However, someone in this planet may argue that Wikipedia has a lower accuracy rate as all the users can remove the accurate article(vandalism) and post some inaccurate article to Wikipedia. Luckily, according to a study which is done by IBM in 2003, they found out that vandalism is not easy to be done in Wikipedia, as vandalism is repaired very quickly, and conclude that Wikipedia has a very good self-healing system.
In my opinion, Wikipedia is better than encyclopaedia in cultural aspect. That because Wikipedia is created by millions of internet users, so we can see lots of articles that are related to sub-culture or internet culture, such as "l33t speak"(f.g.1). And these articles may not be included in some encyclopaedia (fig.2), as they are created by some scholars. I think internet culture is very important, as it can show the moral concept and trend in the internet society, and our children/ aliens can read the articles and know what is the culture in the internet.
I don't know will these aliens accept my idea or not, but if you agree with me, please unite our power by posting your comment, if you don't agree with me, please tell me!