Signal to noise ratio (SNR) "... is a measure used in science and engineering that compares the level of a desired signal to the level of background noise." -wiki How does this apply to advertising?
Well, if I had a client who was a dentist and the phonebook had 50+ full color dental ads and only 5 dentists in that city where on google's first page... Then it would take a significantly stronger signal (read a lot more money and effort) in the phonebook than it would take online to overpower the noise. The less noise (read competitors ads) there is in a space, then the easier and more cost effective it is to get your message out. It's a good rule of thumb to do things differently and to be in different spaces than your competitors. As a friend of mine used to say, "if two people are the same, one of them is not necessary." Save yourself some money and be in spaces that don't require a strong signal to overpower a lot of noise.
There are times when you should jump into the fray. There are some places that are full of your competition's marketing because that's where the audience is. In this situation, you need to be in that space, but be different. Change your radio frequency to rise above the noise.
Suggestions: Be different. Be in spaces where your competitors are not AND be different than your competitors in the spaces where they are.