I've been in First Class (when it was a free trip to launch Wi-Fi) and it's okay, but you're on it for about 15 minutes!
As a result, there's really no point that I can see. Am I also right in thinking they've now made Wi-Fi free for the whole train (or is that a promotion?).
When I came back on it last Sunday, I actually put my bag in the vestibule and sat in a flip-down seat. I couldn't see the TV, but it was quiet (the trains are well sealed) and the seat was perfectly comfortable. For 15 minutes, I'd happily stand! Not that you'd need to as I've never seen it that busy, and if a section is busy (a large group) that doesn't mean you can't walk down a bit.
Anyway - in my opinion there's really little point paying for first class even if you'd just gone around the world and not managed to sleep for a minute of it! Go standard and enjoy first class, which may well just be a good sleep, when you get to Paddington.