As for the webapps: did you create a web app that you yourself would like to have? What I mean is, perhaps you could try to create something that is useful to you, then it does not matter as much if other parties lose interest. Chances are if you like it, other people might like it, too.
A lot of the things you mention seem to be for other people's benefit, not for your own. Like writing papers - presumably the professors have more to gain. Or the science contests - sure, they'd look nice on your CV, but are you also intrinsically motivated to work on that stuff? Perhaps you could focus more on what you like and less on what you think other people would like to see. Just guessing, though.
Another thing could be to "launch" early, so that users keep motivating you.
A lot of the things you mention seem to be for other people's benefit, not for your own. Like writing papers - presumably the professors have more to gain. Or the science contests - sure, they'd look nice on your CV, but are you also intrinsically motivated to work on that stuff? Perhaps you could focus more on what you like and less on what you think other people would like to see. Just guessing, though.
Another thing could be to "launch" early, so that users keep motivating you.