I think it comes down to one thing - how much information does it provide? Not necessarily 'what information am I personally interested in' because my tastes don't agree with everyone else's... but how much information is there that someone else will find potentially useful? I don't think there's any more essential merit in an article about the 'Outer Mongolian horned lizard' or the planet Venus than there is in one on 'custard' or 'love-letters'. They could all be potentially useful to somebody, if they are written properly.

Going back to highschool, in English we were taught that writing was supposed to consider the five 'W's - Who, What, When, Where, and Why? If a wikipedia article follows that policy then I don't see how it can go wrong. I'd think we can also add another one - how? I would see 'how to keep budgerigars as a pet without killing them' as being a logical extension of the article on budgies.

I've posted articles on food and recipes to the wikipedia... and no doubt I'll do more of it, because again I don't see the essential difference between telling you what an ingredient is and where it comes from, and telling you how to use it. The good thing about the wikipedia is that you can do both...