lurker I agree that "poor spelling" doesn't automatically equal "guff" but it does immediately put up at least a partial barrier.
I appreciate I have a slightly old-fashioned view (and no doubt some people would consider it pompous) but my thinking on this is as follows:
If you (generic 'you') are putting something out there that you want other people to read, the responsibility is on you to make it as readable as possible. If you want people to invest something of themselves on your behalf, be that their time, their comments, their advice, their promotion of whatever you're offering etc, then you need to invest a little time and effort yourself making it as easy as possible for them to give it - whatever 'it' may be - to you.
I don't mean every Mumsnet post should be worked on like a doctoral thesis, but a brief proof-read before hitting Post, a quick look-up of words you can never remember how to spell, even just including 'sorry for any typos, am on phone/typing while baby-wrangling' or similar goes a long way and makes it more likely you will get the range of responses you seek. I see it as a courtesy to the people you want to attract to your outpourings.
It's a bit like the 'paragraphs' argument that pops up here from time to time. I admit, if I click on an interesting-sounding title and see a long block of unbroken text, I tend to close the thread quietly and move on as I find it wearing on the eyes to read. I have dry eye syndrome and extreme myopia and my eyes get tired/sore very easily, and I do have a by-now-subconscious thought process along the lines of "if they can't spare the time or effort to hit Return half a dozen times, I'm not going to tire out my eyes mentally doing it for them". The exception of course is if the title or the first line or so indicates that the OP is literally desperate and/or in immediate distress, as only a real dick would focus on the lack of paragraphs in that scenario - although sadly I've seen it happen. What I don't do is post on any thread saying "ever heard of paragraphs, OP?" or "TL;DR" or any of the shitty comments I've seen on such threads; I just quietly move on.
I do appreciate that spelling comes more easily to some people than others (whilst also acknowledging that in my experience, the people I know well who have dyslexia tend to be more careful about trying to spell correctly) and if you could make the effort to be clearer / more coherent and choose not to, that's fine so long as you accept that some people may be put off by it and will choose not to read your post/blog/whatever. (And to clarify - I'm not talking about the odd typo or autocorrect fail, or an odd mistake or two in an otherwise completely understandable post.)