Yes in many cases the true meaning can be understood with the wrong spelling, but in other cases it is critical.
Yes I do believe that correct spelling and grammar are important.
Even when written correctly it can still be open to interpretation. For example, you can spell correctly and understand the use of grammar, why would you need a lawyer.
So I ask, is interpretation of what has been written more important than spelling and grammar?
I know a few wealthy people that can not spell or read very well let alone use grammar correctly but they can count very well and know how to build their wealth.