Open more than one instance WITHOUT Shift

The behavior that you want to change is a Windows Explorer-wide behavior, click on any other icon in the task bar and you'll see the same kind of maximize/minimize behavior. There may be a UI tweaking utility somewhere that will change the behavior on an application by application basis but I've never heard of such a thing. Shift clicking seems like your best bet.

Instead of pinning apps, you can activate the XP-style Quick Launch bar by right-clicking on the taskbar, choosing "Toolbars", and then "Quick Launch". If you then add a Chrome shortcut to the Quick Launch taskbar, it will behave the way you expect.