Most of my work has gone through 15 to 20 drafts before I send it to an agent. It also gets proofread 3 to 5 times, 2 of which I typically pay for. If there are roadblocks that get in the way of the story, you're shooting yourself in the foot, so you have to neutralize that simple stuff.
As far as spelling, grammar and punctuation, what you have to realize is that the proofreading process is not foolproof. When you're talking about 75,000 to 100,000 words or more in a manuscript, 100% accuracy is nearly impossible. Also consider that when a proofreader makes a single change, it affects the entire piece. Change a "character name" to a "she" in one place and it might cause a domino effect throughout the next several paragraphs. Consistency in fantasy or sci-fi can be tricky, too: is it the bluestone of Avalon, or the Blue Stone of Avalon? This is not a perfect science, but if you want to be taken seriously, have everyone you know look your work over and pay a couple of professionals, too! Anything less and you'll be tossed into the trash. It's just the reality. Accept it and meet those standards!