I think the written english is more important. Since the written english cares more about the grammar, which is the basic part in english learning. if you have soild foundation, you do not need to worry too much about the speaking. and why the chinese students do better in written, but like a dummy when speak? it is practice we all know, but the thing is, if you wanna imporve, just practise it, but if you don't have good foundation, how to speak out an sentence?
I know some british locate citizen, they speak english as their mother language, but some of them are illiteracy, cos they can only speak, but not read and write. we call them illiteracy. ok, here, you know how important the written english is, ha?
My point is the language is for use of communication, and how to form a communication? simply say: you know me, i know you. ok, for an conversation, if you two know some key words, two person might understand each other, however, this is only the conversation, which is the small part of communication. if you can not read anywords, how can you understand in paper work? and how to reply? the communication couldn't work out. I donot mean, we can ignore the speaking totally, but the point is which is important,and obviously written english is the foundation.
And i also know some friends have spelling problem, they just couldnt spell, not beacuse they can remember, it is a physiological problem. This problem make their lives difficult, therefore, you know how important is written.
以上是我个人经验及建议,你可以作为参考.