I'd just like to pick up a few finer points of detail to see if I can clear them up.
I can't remember the last time I had anything but a very slow journey between Wandsworth Common and Clapham Junction on the fast line, so losing significant time on that stretch is the norm in my experience.
Yes, this is a problem, especially for some 2C stopping services from Horsham which get stuck behind very busy ex-South Coast services. I do try to report specifics, such as when one of my regular trains is caught up behind station work taking place in the platform ahead, but my understanding is that the broader timetabling can't effectively be made more efficient for at least a few months, given the December 2016 timetable is now rather well on its way. You would also notice distinct similarities with the way 2L services to East Grinstead get held up behind 1A Brighton services throughout much of the day, in the opposite direction. Granted it may not be the case for your trains, but some services have had longer running times added between Clapham Junction and Victoria to compensate, which does at least seem to have done some good for peak arrivals being in sequence. Ultimately, there is also a ripple effect far and wide across the network - for example, if your train is delayed by a 1F or 1H service from the coast, said service ahead will only have got ahead by the margin with which you have created separation by using the junctions at Windmill Bridge or Selhurst. Of course, this means that reliability right down to Haywards Heath and beyond is called into question.
The distinction between standard and first has almost vanished in so many peoples' eyes and enforcement is a thing of the past. Not a single word was announced throughout the whole journey, which finished 14L at Victoria. The scrolling display showed that "this train is ready to leave" all the way from East Croydon to Clapham Junction.
Believe it or not, I've actually noticed a reduction in First Class misuse over the last week or so, and I have no idea why! However, it could just be flukey, though I have been on trains at a variety of interesting hours of the day and it has been an oddly consistent picture. I think the newer 377s are always bound to have more of a problem, to be fair, and unless someone is guaranteed on board (see
sarahj's post), persuasion not to misuse First is going to be very hard.
As for the PIS message, the "Stand Clear" message (or any of the other pre-set messages able to be set by the crew) will not clear until either another message code is entered, or until the PIS functions correctly and displays details of the next/current stop, or until the driver disables all the visual PIS displays (unlikely!). Although it looks illogical, there is no way within the Mitrac system for the crew to get that particular message to clear at a set time/speed/location. The only saving grace is that with so much disruption nowadays, remote PIS broadcasts warning of disruption may be triggered en-route, which can clear such messages. These may occur even at locations when an announcement or visual message wouldn't normally play. But instead, to remove the "Stand Clear" message, the driver/conductor could set a generic one like "Please keep aisles clear [etc.]", which would be announced audibly once, and then scroll visually until the PIS announces the next station. Sometimes, though, with the best will in the world, you just don't remember if you're very busy with other matters. As a member of train crew, you really can be. If that train only had a driver, they would have been...
But one thing you need to know is except for some services staffed by SET staff, no Southern train from Redhill is guaranteed a second member of staff anymore, so there might just be no-one on board to throw folks out of first, or even say anything. Both the 6.51 Viv to Hrh and the 8.12 back were marked as assist for me, so I'f I'm not there, the train will run, but no second staff member.
Almost. Southern services with SE drivers will have conductors (hard to piece together unless you have the diagramming info!), and all services operating between Redhill and Tonbridge have conductors, for the time being, including those with Southern drivers.