I was unable to turn logging on for mod_rewrite.
I tried setting "LogLevel warn rewrite:info" in my_publish.vhost (see core - Apache HTTP Server Version 2.5 ), but my own rewrites would not get logged. On the other hand, default rewrite rules started getting logged with this setting.
Try the following configuration if that helps - LogLevel alert rewrite:trace6
LogLevel alert rewrite:trace6 produces rewrites in error_log. I did not check error_log initially because it was counter-intuitive to search for debug info in errors
As for https://stackoverflow.com/questions/9632852/how-to-debug-apache-mod-rewrite, the suggestion is to use LogLevel in Apache 2.4, which I did
I tried setting "LogLevel warn rewrite:debug" which did not produce any rewrite rules output either.
Mod_rewite is one of the many modules that is installed on apache. You can look at  on enabling logging for rewrite module.
What if you set the log level to more verbose level e.g. debug ?