I don't view bulletin board material as motivational. All players want to win and therefore are motivated.
The problem is focus. Back when I played sports (100 years ago with Naismith), I could get lost in distracting thoughts: stats, nerves, the hot blond in the 2nd row... However, if I hated the guy across from me or someone doubted me I was immediately laser focused. I'm not sure why it did that but it worked every time. Focused emotion is a powerful thing. And since all players are human, they are susceptible to distractions and lose focus.
And that's what bulletin board material does. It focuses you. (Pete Caroll is a master at this stuff). It gives guys a reason to forget all the nonsense and focus on beating your opponent, or just making doubters look the fool.
The Suns have a TON of material to focus them. I trust Monty to put the right stuff up there and get this team, young as they are, focused.