For this situation I would recommend using find. You can specify paths to exclude using the -not -iwhilename 'PATH'. Then using exec you execute the command you want to execute
find . -not -iwholename './var/foo*' -exec chown www-data '{}' \;
Although this probably does help for your situation I have also see scripts set the immutable flag. Make sure you remove the flag when your done you should use trap for this just in case the script is killed early (note: run from a script, the trap code runs when the bash session exits). A lot of trouble in my option but it's good in some situations.
cd /var
trap 'chattr -R -i foo > /dev/null 2>&1' 0
chattr -R +i foo
chown -R www-data *