I guess it really depends.
If you get a chance to actually talk to the DJ/Artist face to face and exchange some info your chances might become a little bit better. I've talked to a couple relatively big artists and gotten e-mails, etc, but that doesn't guarantee me anything.
I just treated them with respect and was a human being to them. I talked to them about my music and they were interested. I try not to flood them with any of my tracks either, because at the end of the day, they still may get dozens of emails a day from other artists as well (and who knows what else), The only time I will send them anything is if it's something I believe has the potential for them to spin live or in a DJ mix.
At the end of the day. They may get the e-mail or it might go in the trash. Stay consistent, but not to an extreme and who knows.