I only care about conversational, but I also think it useful to be able to read a sign while drunk in a foreign country.
if you can speak, you'll be able to read signs and menus and what not. and i'm not suggesting you put blinders on and never look at written spanish. just don't spend any time intentionally working with written language.
i find when people see the written word they are prone to pronounce it as if it were english. where if they just hear it, they imitate what they hear and thus pronounce it much better. i've actually had it happen to me where i've finally seen words written out that i've been saying for years and it'll trip my tongue up and make me mispronounce it even when i know how to say them correctly and have been doing so previously.