Going through the points in order, yes I think your system is more secure than .htaccess over a non-ssl link, because htaccess sends the details in plaintext and those details will work perpetually. The rest of your system may or may not introduce errors which make it less secure, but I don't think that's part of this discussion.

The only gain I could see from encrypting the string is that it will make it more difficult for someone to figure out the algorithm that is used to generate the pseudo-random string.

While you're looking for possible modules to encrypt it though, I'd suggest that you pass over them and head straight for something like Apache::Session::* as a complete solution already checked for problems by someone else.

the hatter