In my experience with Linkedin if you want to make solid contacts, I think that in some point you have to move to the next level and by that, i mean that you have to meet with the one that you´re interested or, if that isn´t possible, establish a different kind of connection.
To lot of people, the only goal in linkedin is to increase to above 500 their number of contacts but they make no use of them.
With that in mind, i find it very useful to network