The saying goes that you can catch more flies with honey than with vinegar.
Does your digital library have some elements (honey) to it that your users will enjoy using? For example, does it include some audio or video -- even just small amounts -- to help capture your users' attention? If your users include children and young adults, does you digital library have some learning games?
Yes, these elements are fun, but they also help us learn. Remember that people -- children and adults -- learn in different ways including reading, hearing, seeing, and playing games.
Reading is what we do most on the internet in digital libraries, as well as looking at images. Some digital libraries contain audio and video, while a few have interesting combinations of the three. Imagine having some audio and video, perhaps brief clips to introduce various sections of the digital library. You might include short lectures that discuss an online exhibit or video that shows the relationship between an online exhibit and one in your library (or the real world).
The audio/video could be changed at set intervals so that users will hear/see something new on a regular basis. The anticipation of new-ness -- the thought that something might have changed -- also keeps people coming back.
It is amazing how much can be taught during a game. You can teach history, language, science... Can you use simple games to intrigue your users and teach them at the same time? Or perhaps you could include quiz-type games that would help users know what they've learned from your digital library. Remember to not make the games too difficult or frustrating. Users shouldn't feel like they are embarking on an impossible challenge.
Or perhaps the game is just there to help users learn different aspects of you digital library. It could be a way of introducing sections, databases or features.
Audio, video, games --> all types of honey. Try them and see what users you attract.