I think it's good to let the developer know what she's doing right, but just bumping a topic with empty praise just seems like spam to me. If you like a project, show your support by helping the maker improve her game, by giving her some compliments she can put to use figuring out what about the game is the best and what might need to be toned up.
I don't understand why people are so big on "motivating" with empty praise nowadays -- I think a lot of it is just done to force out updates from the creator or bump the topic. It'll make the creator go "oh, that's nice of her to say," but it doesn't really contribute anything -- the way I see it, the rule was instated so that both extremes were covered -- if your entire post is "looks good looking forward to the demo," that's about as useful to the creator as "looks bad dont make a demo," isn't it?
There's no harm, but there's no benefit either, and whether or not it's nice, it's still spammy.
Anyway, it's not a big deal, and no warns are gonna be handed out or anything like that -- I just get tired of supremely unhelpful posts, whether negative or positive.