What purpose does this piece serve on our motors? The reason I'm asking is because I'm getting a miss. There are 2 hoses that come off the EGR tube that attach to it. One of my hose came off and wondering if that would cause the miss.

 

that is the sensor that controls the EGR valve, and a line off of that could possibly cause a rough run condition and a miss.

I don't know if it will fix your other problems though, I think that it has its own error code.
This part has a common failure rate too.

 

That is the DPFE sensor. Works with the egr and yes it having a hose off could cause problems.
Dave

 

Did you put the line back on and did it correct the problem ???

And to answer your original question it's spare parts as far as I'm concerned,
all 3 of my Gen 2's have had the complete EGR system taking off.
Looks much better without it and it's much easier to work on

 

Rob,
I put the line back on but have not had a chance to drive it yet.

I should have told Sal when he was building the motor to take all that stuff off.