Sending the same proposal in for every project isn't a very effective approach to marketing yourself in the Freelance graphics, web design or writing business. The very first signal that you're sending to prospective employers is that the project that they care so much about wasn't even worth your time, and the prospect of doing their business isn't even worth you writing a short proposal instead of copying and pasting.
It seems like people do this because they won't want to write at all, but even a little bit of customization can drastically increase the quality of your proposal and elevate the chance of you being contacted by an employer. I have proposals that I use in a template form - I customize them for each job but use the same general outline to convey what I want, and I've found that I'm always getting responses from employers and getting short-listed for projects. As an end result, I have an easier time closing business and getting the employers to pay me what I want.
It recently occurred to me that if I'm getting a lot of job offers, I should be bidding a higher dollar figure, so I've started doing so. My time is valuable and I want to generate as much value as possible in the shortest amount of time. If I'm writing a superior proposal and generating interest from potential clients, that should illustrate that my quality levels are higher and they should be willing to pay more.
I've found that one of the main differences between writers that charge a lot and writers that charge little is actually their confidence in their own work and experience in the industry. If you believe that you're worth $30/hour and you're able to explain why, people will have no problem paying you that much, but you have to set your own standards in order to get there - you have to write great proposals that are detailed and show understanding of the project.
If you invest your time on the front end, you're going to see the payoff later on when you're generating repeat business and being successful.