As you said, you are a student and money is tight. PT 7.4 is more than enough to edit, mix, and become proficient with the software. Save your money, PT9 will not be a huge leap for you. We don't always need the latest and greatest to do our work, when money is an issue, it is best to get by with what you have.
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not only do you get more tracks with PTLE8 and PT9, you do also get a nice collection of plugins that didn't exist in 7.4. also if tomorrow your situation changes and you're asked to import someone's video to work to, PT9 has something PT8 and 7.4 didn't have.. also a more polished interface will have you feeling in a different way. to some people it tends to be important..