Most of the application of Latinate concepts (those systems you mention) to English grammar are pretty faulty. It's what led us down the path to people complain

Most of the application of Latinate concepts (those systems you mention) to English grammar are pretty faulty. It's what led us down the path to people complaining about split infinitives, and all that nonsense up with which I refuse to put. It leads to situations that are akin to someone trying really hard to write a Java program in Ruby. Which isn't to say that learning Latin doesn't improve grammar skills, or push you toward thinking more analytically about language. My argument, though, would be that learning any second language will give you pretty much the same benefit. 5 on AP Latin, here.