It's a big gamble for Orlando obviously, I'm not convinced to be honest. J-Rich seems like the only good and sure addition to their roster but he replaces Pietrus so it's kind of moot (although he is a better player he is inconsistent).
Basically the trades will be successful if Arenas AND Turkoglu get back to their level of two/three years ago... that's taking a big gamble, especially for Turkoglu since he was so great for Orlando because of his duo with Lewis at the 4. I'm not sure the mere combo of Howard/Turkoglu will make him a great fit again, and you also have to simply consider that Turkoglu's game may have fallen off a lot, it's not only a motivation factor or a question of fit.
As for Arenas I really do think that he has more chances of getting his "career level" back now that he joins a winning team. He will be motivated, he just has to stay healthy. Plus he is a clutch shooter, the exact opposite of Carter (in the playoffs).
But if this doesn't work the Magic is stuck with their two awful contracts running through 2013/2014.
Which, by the way, should improve our "chances" (or the speculation anyway) of getting Howard in 2010 since this would give him more reasons to leave Orlando.