OSX Bash for loop - issues with spaces in folder names?
These kind of things can be tricky in all Unix shells due to the way space is acting as a separator, running aliases as part of shell scripts just makes things even more interesting. I would probably run two passes of find to set first the directories in order, and then next the files:

find . -maxdepth 1 -mindepth 1 -type d -exec chmod u+x '{}' \;
find . -maxdepth 1 -mindepth 1 -type f -exec chmod u-x '{}' \;