Overboost annihilator prevents the overboost code from lighting an SES light and defueling. Definitely a good thing.
Hpop Xover... it's up in the air. Some say it helps, others say it doesn't do anything. Usually people see a smoother idle, but no real power increase.
The thermostat deal, some people say they run better at higher temps. I guess it depends upon what you want to do.
Take your AIH Out, and take it to the hardware store. Find the size bolt it will take to plug the hole and then use it. You might want to find some sort of oring to fit around the threads, but that's up to you. Also you can drill/tap the bolt and use it has a boost fitting.