1: 39 in 14 days is quite good. There is 105 members in mailing list - after 2 years....
2&3: My guess is that to choose U++ as your next app platform is quite difficult decision now. And not everybody has the time to play with it right now. So many people download, try, I hope find it quite interesting and then continue what they have done before
4&5: The only 2 things that we can/need to do is to keep releasing new better versions and gain/keep media attention.
The most reasonable investment here, if anybody is interested, is to write interesting articles about U++ and submit them to various websites.