Well, I think it's definitely one of those things that requires high amounts of dedication. And, well ... I lack dedication a lot of the time, so it's rather fitting that I don't make them.
I wanted to make a "huge RPG" as well (and I am actually in the process of doing so, sort of), but I've decided rather than going the usual RPG route of one main storyline and then jam-packing the rest of the game with barely-related sub-quests I am going to create the game like comic book issues.
Most comic book series build up their universes issue by issue gradually covering more ground and the stories are fully contained within the issue (usually), so you are not generally bombarded with a bunch of plot-lines going every which way (unless we are talking Marvel or DC which have so many fractured and broken plot-lines that will make your brain bleed).
If you ever get the chance read the Usagi Yojimbo series by Stan Sakai, his pacing and plot-lines are amazingly solid (probably because most of his inspiration comes from Akira Kurosawa movies, speaking of which watch Seven Samurai as well). Dragon Quest 8 really had that kind of pacing too. Even though it was one huge story you were really playing a bunch of short stories that each wrapped up nicely while subtly advancing the major plot-line.
Anyways, you can make a huge RPG a lot more manageable if you build it up in "issues" or episodes and let the world grow out as necessary. 5 episodes in and you'll have a pretty good-sized RPG world. As an added bonus, you won't need to create as many resources to make one episode as you would making one huge story-branching RPG (and I believe there are means of transferring data from one RPGMaker game to another, i.e. between episodes).