You can share code between projects by having seperate visualstudio projects that create a managed library. just put the managed library into your assetsfolder. it live reloads as smoothly as when you edit just one script.
While I'll be the first to admit that we have some things that you can consider basic that don't work as well as they could yet, the perspective from inside the development team is that we have an enormous focus on improving what we have, and do not do "jump on new feature, and quickly move on and forget about it".
@reitzensteinm, We would love to fix your crash! If it happens in Unity4 as well, it would be great if you could file a bug, or give us some way to reproduce the problem. While we think using our serialization system makes a lot of sense for most games, we will always support people wanting to do things in their own way, and serializing your data with json should not be a problem. obviously, you crash and there is a problem, so we'd love to get our hands on that and fix it!
Bye, Lucas Meijer