Invest by contributing for starters. Second, by maintaining them. Exactly the reason why a lot of profiles fail to be an active part of a network. They are not maintained, updated, nor do they provide content from which others benefit on a frequent basis.
In my opinion, the trick is to find your 'best-practice' friends - 'best-practice' customers if you will - in social networks and just start communicating about mutual shared interests.
If you're interested in a lot of things (like me) it takes more time and effort to get through to people. In general, people like clarity. Being interested in multiple subjects obscures their image they want to form about you. In this case you might want to consider segmentation, which I am doing. Build more networks than just one. It will take more time to keep them current. In return, however, you get to share all your interests (all my...) with likewise minded people.Build Your Networks Before You Need Them