I had the problem too, that dpkg-reconfigure didn't write a new config file.
By chance I found out that you have to use the tool called "dexconf":
:~$ dexconf --help
Usage: dexconf [OPTION ...]
write an Xorg X server configuration file based on debconf database values
Options:
-h, --help display this usage message and
exit
-o FILE, --output=FILE write configuration file to
FILE
This help message is intended only as a quick reference. For a description of
the usage of dexconf, see the dexconf(1) manual page.
Could have saved you a lot of work ;-)