Encryption wont make any difference on a forum this old and brittle.
They are orthogonal in what encryption can achieve. The implementation can, indeed, sometimes will fail with an old forum like this without significant investment, even the TLS connection terminates at the edge (webserver/proxy) then forward to vBulletin. Then the next is to take care of all non-https active and passive contents on the websites (e.g. css, js).
But we should try anyway, with just enabling HTTPS on visit means we can be certain about traffic between user and the server is secured and encrypted...
I thought we went over this last Fall... anyway, I don't think admin would invest in this.