basically a power boost valve is a way of turning up your fuel pressure.
in the right hands and on a well set up engine that has had the airflow increased to match it can be useful. if fitted and not mapped for the car though can have a detrimental effect and may make the engine produce less power.
benefits can be found on some cars though. i know of a few people that have done the usual 130 bhp upgrades to 1.8 escorts i.e cams, throttle body, mass airflow sensor etc and incorpated a power boost valve into the build before getting the car sent off for a remap. these have come back with a lovely power curve with no flat spots. very nice to drive in the road.
in a word yes they are useful if used correctly.
as for the ecotek valves they basically fit into a vacuum pipe going into the inlet manifold from brake servo. this creates an amount of turbulent air that is meant to have a positive effect on the way the air and fuel mixture is delivered. results vary on different cars. most people say they notice better fuel consumption, some say they erradicate flat spots through the rev range, some notice no changes. all down to personalpreference really. the best thing to do is try and borrow one and see if it makes a positive difference to your engine.
hope this helps a little

ian