Usually that would be enough, but you have to remember what is spam or an 'abusive comment' or post that doesn't make sense to you might make sense or be completely valid to others.
I understand the fact that what I may find spam, the MODs may not find it spam and hence my percentage is dropping.
However, some members make
personal comments/attacks on other users, make bad comments about religion, help others to commit suicide, talk about drugs and so on and I report all those comments but I find that the reports are excluded and so I don't get what can be the reason as they being considered "BAD."
None of theose things are against the rules as long as they're on topic and in the appropriate threads/subs so you will get a bad report for them.
Also, what if half the number of my reports are "BAD", will the MODs start disregarding my future reports?
No. It might effect your chances of ever becoming a mod if your accuracy isn't very good though (if that is something you would be interested in).