It depends one what the Raiders long term strategy for the position is. The Raiders are a long way from being a competitive outfit. Flynn should give them some nice play and warm the hot seat for whoever is going to be their LT #1. They have every incentive to continue their level of mediocrity in the hope of landing a Mariota or Manziel.I was a bit surprised to see it become more and not less, but then when you think about it that really isn't much to pay your starter either.
They decided to make him their starter for less than 1/2 the money they were going to pay Carson Palmer. Do we really expect him to be much worse than Palmer? In the meantime they saved a lot of money and potentially improved their starting QB situation.
As for M.Flynn, he looked like he at least belonged in the 2 games he started. When you throw for 433 and 518 with a total of 9 TD's in two games, people tend to think you may deserve some more reps. On top of that he certainly didn't appear to be frazzled in his rookie start on the road vs a veteran coach in Belichick under the lights of MNF. That has to count for something to in the minds of scouts and GM's.
All that said, I still don't expect him to succeed all that much because the team around him totally sucks, but he should be able to do at least what Palmer did for less than 1/2 the money.