How do you know when a crush is worth a shot?

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Basically I've been falling on and off for this girl for nearly 3 years since our first year in college.

The thing is that I've never actually talked to her beyond trivial shit like "do you have a pen" or whatever. I've probably never spoken to her for more than 5 seconds.
I know she's pretty, she has an obvious passion for gymnastics (it's not that it's gymnastics specifically, I just find it awesome when someone is passionate about something) and she's a hardworking student, which I admire and respect a lot. But that's just it.

Some days I don't give much of a damn about her, other days (like today) I find myself nearly sinking in a pit of melancholy, regretting that I didn't get to know her, that I can't have her, that I don't even have her as a friend.
Another thing I should mention is that she's graduating this year, whereas I'll be staying for another year so I'll probably never see her again. This only makes me want to go up to her and tell her to her face that I think she's cool and cute, but my dilemma lies in that I am not sure myself if this crush is actually deep enough for me to go out and pursue it because, like I said, I don't even know the girl personally.

tl;dr:
>been crushing on girl I've nearly never spoken to for almost 3 years
>want to confess but don't know if it's actually worth it (in that maybe my brain is just being dumb and this crush is superficial)
what do, /adv/?