There's a lot of varying opinion about this from other, non-RPG Maker communities. When it comes to other types of games, demos are often never even played--or if they are, they lower sales because a player will play them and might decide the demo isn't fun enough, as the demo just shows the basics before things get interesting. Or if the game is simple enough, you can just keep playing the early levels and have no need to even buy the full version.
RPGs, such as ones made with RPG Maker, tend to be a bit different. There are a fair amount of people excited to play the demo of a unique new game, to see what's possible with the engine and to explore the start of a cool story. I like games that are all about making progress, and a demo will likely leave people with the desire to buy the game.
So when is the right time for this demo, assuming it's a commercial RPG Maker game? I notice many people get their demo out as soon as possible, then proceed to take a year or more to actually finish the game. On one hand, it's useful to get something out there early because you can gradually build up a small community of supporters who have liked your demo and look forward to updates. But others mention that things will inevitably die down after awhile, and all the hype of a new demo release could fade. So would it be wiser to make a demo further down the road, when you're going to be putting the game up on greenlight or even make a kickstarter? But there's a value to early feedback too, and people's feedback can positively influence the rest of the game. If you make a demo just before the game is going to come out anyways, you can't exactly make changes.
An option would be to still put out information about your game, post screenshots, explain its features, and then just share little demos with friends and they can playtest for you. You can still build a fanbase that way, but it's likely you'll have a few people asking for a demo.
So anyways, what are your thoughts? Release a demo as soon as you have the content for it? Or wait until you need the hype for it, like during a major advertising campaign? I'm interested in seeing the discussion behind either method.