In my mind you have to do something like this:
- Lets say you have two paths for your repositories:
/var/lib/svn-secure for the repos you want to work over ssl
<Directory /var/lib/svn-secure>
SSLRequireSSL
(... snip all the SVN config ...)
</Directory>
/var/lib/svn for the repos you do not care if they are over ssl
<Directory /var/lib/svn>
(... snip all the SVN config ...)
</Directory>
then you create two virtual hosts, one over ssl and the other plain text. and put the locations in the respective ones, the SSLRequireSSL will force the access to the directory to be done over over ssl or will deny the access.
Be warned, I did this from the top of my head, there might be syntax errors.