I'd loved to have exchanged emails with you a year ago.
The admin is amazingly malleable. Almost everything can be overridden and replaced. There's plenty of nice debugging/logging solutions (Werkzeug+Django Extensions being my favourite). Email switching between dev/producution is trivial (unless I'm misunderstanding you).
There ARE some clunky parts to customizing auth - mainly around extending the User model - but it's not that terrible.
Yup, just as I say, I'm sure there are solutions to these things if you know the answers. I did look long and hard at the time though. We were using a version of Django where the auth/user stuff had just changed and there were no good examples of how to extend the user model (frustratingly there were good examples for the previous version).
Regarding the email stuff, my criteria for a framework is that I'd like it to send real emails on live and fake ones on dev. That is, email everything to me on dev along with a little header showing who the email was going to etc. Invaluable for testing.
It's a typical scenario really. On the surface it gives you a great framework for creating a website that works in a certain way but if you deviate from that you tend to find yourself in trouble.
In our case it was mostly the admin section that created the issues. I'm sure that if you know the framework well enough there are ways around the inflexibility but the fact of the matter is, the Django admin is heavily based on configuration. Where you have configuration you have limitations.
Things may have changed (it was about a year ago when I last worked with it) but at the time I struggled with simple things like; customising the auth system, easy debugging / error handling, clean outgoing email switching between dev / live, the templating system, etc. I seem to recall spending most of my time ripping code from the core framework into my views.py and tweaking it so I could get the behaviour the client was asking for.
As I say, it's been a while since I worked with it and I'm sure people have solutions to the issues I encountered but if you're planning on going off piste at all it's probably not for you.