This is a major problem. I agree with you, and I don't see myself writing a lot of Arc scripts in the current situation.
Maybe a client/server would be a way to solve the problem. I may try something like that one of these days. I mean, launch Arc once as a daemon, then talk to it with a lightweight client, via FIFOs (named pipes) or something.
For the moment, you may want to comment the imported arc libraries you don't use (in libs.arc or as.scm), for instance all the HTTP/HTML stuff. Loading only arc.arc, my load time is reduced by 50%.