As it was already said, it is hard to tell without knowing more, however, I am going to try to answer keeping a general view, and understanding from your post that you shoot street photography, as you say you do a lot of photography in the street.
I know lots of people are going to disagree with me, but I greatly prefer prime over zoom lens.
I am a big fan of Henri Cartier-Bresson (who can be consider as one of the most (if not the most) influential and talented street photographer); whenever he was shooting for himself, he would use a 50mm, so his camera can really become an "extension of his eye". I personally think that he was right in doing so.
Prime can have much bigger maximal aperture than zoom; I personally don't know a zoom lens that is faster than f/2.8, but know a lot of f/1.4 prime. Bigger aperture can not only be useful in low light situation, but gives you more option in term of depth of field control. Everybody love bokeh
Also, they tend to be sharper or/and cheaper, however, this is not always the case.
Of course, having access to multiple focal length is extremely useful; zoom lens are far more practical that prime in that regard. However, I tend to think that limiting yourself to only a few focal length gives you the opportunity to master them. I personally view photography much more as an art form than a business form (this is really just my opinion), so the usefulness isn't all that important compare to the possibility of growing as an artist.
Ultimately, the most important thing to keep in mind is that what really matters is which lens you prefer, even though I am sure that you will get some awesome advices from this forum. In street photography, I think the best focal are 50mm, 35mm, 85mm and 135mm. However, everybody as their own view and their own preference, depending on their style and their view of what is photography in itself. This is, for me, an awesome thing; people having different view and preference is one of the reason why, after nearly 200 years, there is still lots of great and unique photos taken nowadays.
In summary (sorry for the long text, I hope it was not too boring!), if I was you, it would use that money on a few fast prime. The 24-70 II is about 2300$, so that leaves enough money for some good lens! If you are into manual lens, Zeiss are close to top (a poor man choice would be Samyang, which are extremely good for the price!). If you prefer lens build in a more modern view, I heard great things about Sigma 35mm and saw great things about Sigma 50mm f/1.4. Also, the Canon 85mm f/1.8 is one of the best values IMO in Canon's lens.
