A question to lowering the compression!
I install a 2 mm or more copper head gasket ?
Loss power at the lower rpm's , and this results a wider powerband ?

I'm not sure of the proper way to lower compression, but I would think that it requires modifications to the combustion chamber in the head as opposed to a simple spacer.
Using just a spacer might cause problems with the squish.
A copper head gasket might cause more headache than you want...they're impossibly hard to seal correctly.
If you have the combustion chamber in the head enlarged for lower compression, you would still be able to use a standard head gasket or have it O-ringed instead.

Lowering the compression would result in less power overall, and theoretically should be able to rev higher (but that's just one small factor in how high an engine can rev).
How it will affect the powerband is anyone's guess, it depends mostly on the rest of your setup and how it's all tuned.
The biggest benefit to lowering compression would be the added resistance to detonation and lower mean effective pressure, both adding longevity to the engine.
One added benefit...it'll be a little easier to start!