As far as leachate is concerned there is a lot of debate on how beneficial it is. Yes, it will contain the good stuff in vermicompost dissolved in it but what it is composed of varies so much in different systems or even the same system at different times.

For example, if I have a bin full of finished VC and pour water through it the leachate should contain a lot of the good stuff from that VC. Pour water through it again and it should contain less and so on. Kind of why I don't think the O'Donnell system is what I would want. Really, it's a rubbermaid with a spigot but I don't think that pouring water through the bin and using the liquid gives the same consistent results as top dressing plants with VC.

I just throw any leachate on my trees so that it isn't wasted but as far as how much benefit the trees get, well it depends. If I feed a lot of watermellon I get a little more leachate but the state of decomposition and amount of VC in the bin doesn't change much.