There will be no impact as the svn client shouldn't be running continuously as a functional part of your website/server.
A 1.6-> 1.7 upgrade should be seamless; just be sure that you don't have any pending changes to commit (commit before upgrading). Run svn upgrade
immediately afterwards on each working copy to update the metadata to the new format/structure.
However, you're upgrading to a version that's several years old. SVN is on 1.9.x now. I would recommend that you upgrade past 1.7 to 1.8 and then 1.9 so that you're on current software. At each stage, run svn upgrade
on the working copies to get the metadata formats/structures updated to match.