Not to over-labour a point, but am I the only one to have run into trouble when I've seen a game is likely to be "easy" and therefore not done this? I'd much rather go into all games on high alert, jump on the first few poor tackles or low-level bits of dissent and assert the level I like to work at - and I don't need to know what mood the players will be in to do that.
Again, the bits I've underlined are all things I do - I just do them consistently in all matches, rather than putting the effort into "difficult" matches and relaxing and assuming "easy" matches are ones I can coast through.
I'd argue that's a different thing to pre-match research, and therefore a much better indication of what's going to happen. In fact, I'd go as far as arguing that pre-match research will probably hinder your ability to do this in a balanced way - if I turn up to a match thinking that the red team is going to be trouble, it's going to be very hard not to keep a closer eye on them and neglect observation of the other team. If I'm staring at the red team trying to work out if number 8 is in a good mood today or not, it frees up less time for me to notice that at the other end of the pitch, blue 6 is hungover/drunk/raging at the world.
Alternately, I can turn up with an open mind, keep an equal eye on all players and have a reasonable idea of what mood both teams are in.