Better to send one than not. Many HR specialists will voice the opinion that cover letters are not read and that they have just too many resumes. When in doubt, send a short note anyway that adds relevance to your resume and shows that you want to make a strong first impression for the company.
Stay away from dreams and philosophies. In other words, think about what this employer really wants, read the job description and study the company website to get clues on the type of employee the company wants to hire. What can you do for them that will improve their initiatives? Why are you passionate about applying for this position?
Spell check and have someone proof for grammatical errors that you may have overlooked. Have a trusted mentor really give you honest feedback on the content. Does he or she want to ask you to an interview?
Try a new approach from the tried and true when closing. Yes, hiring managers are busy and many will respond with a message not to call them but they will call you. However, if that is not an issue, set up a date in closing that you will be following up with them and make sure you try to contact that individual or department at the designated time. Don't hound or appear desperate that you are going to follow up the next day but call back in a week to see if there has been progress when reviewing your resume and application. It shows that you are worthy of your intentions and that, alone, is a reassuring quality for any position.