I am a driver and actually think it would be quite beneficial for guards to have at least one trip up front whilst in training or as part of their route learning. We could then point things out from our point of view and it would help the guards see why we get tetchy at certain things, for example if we get buzzed off against a red or without an RA if one is required. We could point out various useful bits of information which probably get overlooked in guard school which could come in handy. The more other people know about my job the easier it is for me, that goes for signallers, route managers and even company directors.
I had a network rail area manager ride with me once (legal and above board) to check part of the line which had been reported as rough riding. Whilst up front I was explaining bits of the route which can cause problems, particularly badly sighted signals, areas where vegetation needs cutting back before the Autumn, an inexplicably placed whistle board etc. He explained a few things to me and we both found the trip to be beneficial.
Common sense and good cab discipline negates most of the distraction concerns as far as I'm concerned, that said my job is important to me so nobody comes in unless its above board but I do think guards should have at least one trip up front with us.