I personally change the network settings manually with an editor, but I think
netconfig is the only text-mode tool to do this, so...

1) netconfig should have an option that it wouldn't rewrite /etc/resolv.conf.

This is needed on systems that want to use netconfig to configure non-primary interfaces.  
You can avoid this by setting the correct DNS server for every interface, or not using TUI, 
but a real solution might be in order.

2) netconfig should report if invalid options were input.  That is, if you e.g. say:

netconfig -d eth1

Whoops!  The correct syntax was -d=eth1 and netconfig just silently discards the option, 
killing your current eth0 setup (and connection).

In a similar way, something like netconfig --uasdasvaslkdfvla doesn't give a complaint either..