He gets shit done, he has gained a remarkable amount of influence all over the campus with multiple important people and she seems to want to use him as some sort of muscle. Also manipulating people to do what she wants can be a reward for her by itself.
Granted there are some indications that she might soften up to the MC somewhat. It will all depend on how DPC wants to write her.
she could easily get that from the jocks or other people on the campus
want muscle? use caleb or other gym rat from the jocks
want influence? there are a lot of people with more influence than MC, rusty and tommy, dawe (now being the the jocks president and having a gym), the preps, etc
im not gonna say that quinn is not going to use MC for some "jobs", i think that downtown date is probably to protect her from being robbed again but she also likes MC and be with him, its not only to help her out.