I use to get contract work through agencies. You need to develop a thick skin in dealing with them.
The first thing is not to take it personally. Using agencies is very impersonal and for most of them you are just a number, you need to get over that. If they have something for you, they'll get back to you. If they don't they won't its that simple. Most of the time you never get a reply. In return I don't waste my time replying to agencies generic emails, unless its specifically targeted to me, and has a job that is close to what I'm looking for. Most are just cold calling, and its waste of your time replying.
The second thing is theres a lot of fake, old, and duplicate jobs on these websites. From experience, real ads with have weird requirements, something different about them, not just a standard spec, and there won't be 20 jobs, with almost the same spec. After a while you learn to filter these copies. Also jobs can be duplicated across difference agencies. I don't know why companies do this, but again learn to recognise very similar ads, even if they are different websites, its probably the same generic ad. If you go to company websites, and places like FAS, they generally have no or very few agencies, and jobs have salaries listed, or quirky details which also is a sign of a genuine jobs.
Put more effort into researching companies that have jobs that match your skill set, and asking around everyone you know, and traditional paper adverts. As these are as as successful if not more, as using agencies, or the internet and people forget and just stick to using the internet. The old job hunting methods are still very valid. A book like what colour is your parachute is useful. You can get it in your library.
I'd advise against dumbing down your CV, and also against talking it up, embelishing stuff. Instead, keep it as simple, and concise and brutally honest. That worked best for me.
Finally don't spend all day job hunting. That wrecks your head. Dedicate a specific amount time, and after that go do something else, take your mind off it.