It's this kind of sloppy compromising which damages the end user experience. Cutting corners shouldn't be an option if you want to present yourself as a professional at what you do. Accessibility validation tools aren't some kind of simple quick patch until you get round to doing the job properly. Either your website is accessible, or it isn't. There's no meeting it half way. While I understand your reservations towards manually doing anything that may be able to be checked using a piece of software, it's a simple fact that disability isn't something that can be measured and replicated effectively using computers. There are checklists for WCAG, tonnes of articles and tutorials on web disability, great books on the subject... why compromise your audience with a half-effort attempt when you can maximize the visitors experience.
Technically, several real people with several real disabilities are the best option though it's not always possible. I always say the key to understanding disability is to emulate the limiting factors yourself... browse the web with the monitor turned off to experience blindness, turn off speakers for hearing loss, browse while "hand trembling" to experience motor function deficiency (and perhaps via speech). Be creative in your approaches but whatever you do, ensure your website is as seamless for people as possible. You need to consider how people input/output against machines and determine their complexities.
Section 508 is built upon WCAG, its the most definitive example of recognised factors that affect users on the web. However it's worth mentioning that WCAG isn't perfect in itself... it doesn't cover disabilities like dyslexia, lingual issues, computer disability or mental health impairments. Disability is anything which can inhibit the end user, whether physical, intellectual, emotional, social, psychological or mechanical... a broader perspective if required when testing for completeness.