Adding plugins does not create more “processing”. This is a misconception of the way PHP works.
There is a certain amount of overhead in reading files in, yes. However, this is small by comparison to the overhead of compiling and executing the code. However, PHP does not compile code until it actually runs it. As most plugins consist of lots of added functions, those don’t add any execution overhead until they are actually used in the course of things.
Installing Viper’s dashboard widget manager will not add any extra processing worth mentioning. It will only run when you pick it from the menus, and then it will simply let you adjust the dashboard widgets.
Also, if you use this plugin to adjust the dashboard and remove those widgets, then they won’t be executed anymore either, because they’re not on the dashboard. It doesn’t “hide” them, it removes them. In much the same way that the sidebar widgets don’t run unless they’re actually in the sidebar.