I've been using Nuget.Package.Builder (a Nuget package by Lars Skovlund) which turns any class library project into a Nuget packager producer for years. So you only have one project, not two. Is there any benefit of NuProj over Package Builder?
His approach adds a bunch of MSBuild code via a .targets file. I really like the purer approach that NuProj takes, but its a pity that it needs that extra project for every Nuget package (unless I'm woefully misunderstanding something)
Oh, and for open source stuff I've been using AppVeyor to create and push the packages