Short answer: here.
I now proceed to ignore your question and instead look at what I think is the motivation. If you want to moderate the site based on flags, I say go for it. If the mod team thinks you are flagging far too much, we'll let you know.
You ask about bad questions/answers and flags. In many cases, the correct behaviour for bad questions/answers is to leave a comment and downvote. Mods do not delete content merely for being incorrect, for instance. This might be confusing, but our role is to moderate the site, not guarantee correctness. You shouldn't flag something merely for being incorrect either. Explain why it's wrong, downvote it.
You also mention the spam flag. Spam has a distinguished meaning. For a post to be spam is for a post to be an advertisement or link to a page/product(s). If you flag merely low-quality posts as spam, your flags will be rejected. Similarly, if you flag merely low-quality posts as offensive, your flags will be rejected.
Finally, I want to add that there are many more ways to help moderate the site than by flagging. Some of the most important tasks are janitorial and lead ultimately to better site navigation. These are less easy, and therefore we are in constant need of help. They're also important which is why they're incentivized by badges.
Edit questions to have informative titles. Titles should accurately indicate the question. For example,
A calculus question is a terrible title.
help exam soon!!!! is worse. Edit these away.
Edit tags to properly reflect the question. Add tags, remove tags, use more than one tag --- that's all fine.
Identify and mark duplicate questions as duplicates. If a question should be merged into another, flag for it.
Upvote correct, unvoted content. (This is a recurring theme of mine)