The resume is a single piece of the process. For me to open a resume, first I have to open an email. How long does it take to write a couple sentences to make me want to open your attachment/link?
Then on the resume itself: write a summary. Don't make a recruiter (who 6 months ago was a "struggling unemployed kid who took the first job offered") try to interpret that you are an experienced $LANGUAGE developer with n years of this and that. Come out and tell them exactly what they want/need to know in order to make the decision.
We generally have underqualified people reviewing resumes for companies (agency recruiters, HR, admins at startups). Don't give them an opportunity to mess up. The job says they want a "Python dev with >5 years and some experience with Django"? Tell them exactly that in a sentence in the email, and again as a summary statement on top of the resume.
This isn't 10x effort. It's minimal. It's the hiring company's fault whenever someone qualified doesn't make it into the interview. My philosophy to my resume clients is "don't let HR screw you over - hit them over the head with your qualifications and they can't say no".
And very few of the targeted companies got back to me. I now work at a place that got my generic career fair resume and had a pretty plain "I hear you know how to program?" interview...... Fantastic place though, wouldn't trade it for a 5x pay increase. :)
Having actual paragraphs combined with the keyword jumble goes a long way. You don't have to do excessive customization for each job.
This is the theory, yes. In practice, that 10x level of effort is not matched by a 10x increase in the number of interested responses or a 10x increase in response rate. Diminishing returns sets in quickly. You wind up with more interested responses by shutgunning your resume all over the place - assuming you have a good resume.