With the way defenders are paid on the open market these days, and given Philly's apparent need to sign a good defender, he should get those numbers easily either from the Flyers or the open market. But it's unlikely that Streit gets to July 5, as if it's money Streit is seeking, Philly will make every attempt they can to get it to him. Last year, they attempted to offer sheet Shea Weber and the Streit trade seems to be this year's strategy to obtain a defender. They'll just have to clear cap space, which will likely happen by buying out Ilya Bryzgalov.
For the Islanders part, a player and fourth round pick is a nice return for a player they could not come to terms with (there's an argument to be made that they could or should have paid more to Streit, but once the decision was made not to, this is a fine route to go). And there will be defensive depth coming this fall and next to replace the aging veteran. In the trade they got a free pick in the draft and a free player although the player, Shane Harper, could be more of a throw in that Philly needed to get rid based on their contract situation and is a restricted free agent that the Islanders don't plan to qualify.
Harper, it seemed, knew as much yesterday when he talked to Michael Cignoli who covers Harper's AHL team, the Adirondack Phantoms (he was also demoted to the ECHL during the season).
According to Cignoli, Harper was unsure of what his future held. If the Islanders don't qualify him, he'll become a free agent: “That’s kind of what I’m worried about. My agent said [the Islanders] have a lot of contracts and they've been actually not qualifying guys as of late... I’m not really getting my hopes up, but that’s what I’ve heard from my agent. I might just be a free agent.”
The Flyers contract situation is a mess; they're right up against the cap and need to cut salary to sign Streit. Philly has 43 contracts towards the maximum allowable mark of 50, and that doesn't include Streit or any other impending RFAs or UFAs they may re-sign (Flyers perspective here).
For the Islanders, they're at 33 contracts, plus at least seven players they are likely to re-sign. They might have room to qualify Harper, but it's likely not worth it for a player demoted to the ECHL last year and lots of young players knocking on the door.