There's only a few (great) people on there that have been mods longer than me, so here's my take on it from years of digesting it, in my usual assorted, scattered order:
1. Not everything that is reported needs to be moderated. There is a lot of grey area on this site, as there is on most sites, and in the interest of wanting to be fair to posters and not be ridiculously heavy handed, most mods will give posters the benefit of the doubt on the front end, maybe with removing a post and a warning or something similar. That means that the post that you reported maybe didn't get removed, but another one did, and the poster in question got the official message to knock it off. That might give someone the idea that the reporting is being ignored because they can't see the post(s) that have been removed. Generally most of us aren't going to go through the guilty party's profile and take down everything that qualifies because it takes a lot of time and effort, and most threads have an extremely short shelf life - no one is going to remember it or see it a couple of days from now. Which brings me to
2. Threads with a lot of active participation are going to be moderated more heavily and regularly than those with 1 or 2 posts. If no one, or virtually no one, is seeing it, it's not a judicious use of time to spend all day taking down people shouting in empty hallways. We (collectively, I speak for all of the mods here) would rather keep the active and engaged threads clean if given a choice.
3. Spam and spammers evolve - their techniques evolve, the posters change, the things that are being spammed change. Mods aren't always immediately hip to the latest scam flavor or spammer, so you should continue to report posts even if it seems like no one is listening because it helps all of us get better at spotting the guys (I'm from NJ, this means women too) who are clogging up the airwaves here.
4. More Mods won't necessarily change things that are complained about, because as my esteemed colleague @Nathan Gesner mentioned, it depends on time of day, forum(s) frequented, posting times, and other issues that sometimes means there's a whole bunch of us here at the same time and sometimes I'm the only guy here, or Nathan might be, or Ned, or someone else. Theoretically more Mods means more chances of catching stuff, so more help is generally always welcome, but no one should expect miracles.
5. The amount of spam & scams ebbs and flows in response to things that might have little to do with BP, and again sometimes that means response is a trailing effect. We (mods) will have a trainload of spammers, and all of us are doing double-time clearing things off, and all of a sudden it will get real quiet and we can go back to doing things that are usually more fun like posting and reading threads, which doesn't mean we become complacent but does mean maybe we're not as vigilant as usual.
All of that means you should continue to report anything you see, don't become disheartened if not everything gets taken down, and mostly just ignore the noise. I scan the forums every day, but I mostly ignore any threads that seem like a waste of my time either because they've already been fully answered, they're spammy in nature even if not explicitly against the rules, or they're just not something I'm interested in. If most people do the same, a lot of the scams & spams take care of themselves because there's no audience.