How to establish collaborations with academics who you do not know where you contribute to their research projects? Lately it feels like I haven't been doing enough both personally and professionally. I am very productive at both my place of employment and my graduate studies (i.e. PhD in Soil and Water Science) however I want to be more active. I am perfectly content with crunching numbers, developing models, researching the literature, writing up results, etc...I know I am kinda...well nerdy and weird that way. 

Recently I have begun reaching out to scientists in my field asking if they would like to collaborate in an effort to gain more experience with different kinds of data and ecosystems, make more connections, etc. When I offer to collaborate most don't respond...which I completely understand being an overworked scientists in the publish or perish game who needs another person to slow you down? Meanwhile some respond with a "sure love too" then when I follow up with questions or brainstorming ideas no one responds. 

Is it proper to email say a professor with an email indicating that I am interested in their work and would like to collaborate on any projects? If they respond with a "Yes, love to work with you" type email with subsequent emails falling on deaf ears, is it them nicely trying to say bugger off?
Collaborations almost never start with a cold email in my experience. All of my collaborations have involved people from my former lab, people I met at conference, or an obvious opportunity where I had the data and they had the analysis tool. Anecdote aside, I think you have to have something the other side will obviously want: a dataset, a method, a tool; access to a site or species or specimen; something besides an idea. Lots of people have ideas. Lots of people even have the same idea. But in order to start a research relationship with someone you don't know, you've probably got to have something they want and vice-versa.