I would love to hear others' responses to this because I'm in a similar stage of the game as you, probably a bit further behind actually.
I think I'm a little different than most, but my response is actually send away. If you are truly creative, then there is a lot more creativity you will be able to contribute, and if it gets you more known, then its worth it. Personally, I'd love for a Top 40 artist to steal my beat! Sure, I might lose out on royalties from that particular song, but it would sure boost my resume.
I know there are some that feel that a producer shouldn't undervalue themselves and just give stuff away, but if you think of it from a business perspective, its just a marketing strategy. Actually, my understanding is that more and more record labels are starting to consider recorded music as just marketing material anyway, meaning that they expect to make more of their money from concert sales, side sponsorships, etc. than from dwindling record sales. Following a similar format, having a few folks steal my tracks would be well worth it if it brought my name up. If they're big enough for me to care, it will be a resume builder. If they're not, no skin off my back.
I guess it depends on how well known you already are - if you have already had several major placements, I would think it would be a huge mistake to send out beats that could be stolen. If you're still struggling just to get know, I would say put stuff out there.
One thing is for sure, though - if you put stuff out there by just emailing it, expect full well for it to be stolen.