I don't think it makes sense to move Brodin, unless we get something pretty impressive coming back. As good as Middleton has been playing this year, he is a middle pairing guy, who can't defend speed very well, and is limited in the breakout game. Also, Brodin's 6M cap hit will seem more and more reasonable as the cap continues to climb. Buium might end up as a 1st pairing guy, but he will likely need 2-3 years of seasoning and being sheltered, and with Jiricek also needing the same, losing a defensive rock like Brodin could hurt us.
Spurgeon, OTOH, is a different case. Faber is a direct replacement as #1RD now, not at some hypothetical future date. While Spurgeon is better than anything else we have at #2 RD right now, a combination of Bogo, Jiricek, Spacek, and a LHD (chisholm/Brodin) playing on the offside can fill in for him. Spurgeon is more expensive than Brodin, and his body seems to be falling apart a bit. While he is respected in the dressing room, and loved by management, there comes a time to be a cold hearted SOB and trade the guy if there is a deal to be made. That extra 7.5M in cap space(replaced by ELC Jiricek, or RFA Chisholm $$)would come in very handy.
Middleton - Faber
Brodin - Jiricek
Buium - Bogo
Chisholm
The above is not too bad. A lot depends on how Buium and Jiricek pan out, of course, but it's well past time that we stop stockpiling D talent and get some depth up front for a change, instead of trotting out players like Johansson/ Hartman/Foligno/Rask/Gaudreau and pretending like they are top 6 options.
To be clear, I am a Spurgeon lover. I think he is, or has been a terrific player for us. I just think that all well run teams have a hint of ruthlessness in the FO, and must think of the future rather than dwell on what a player has done in the past. Paraphrasing one of the all time great GM's, "It's better to trade a guy a year too early, than a year too late."