cant really say what boost you get when winding the standard actuator to max as i have fitted a garret -31. im using little less than half a hole preload and im getting about 0.6 bar with the amal valve disconnected.
Maybe your spring inside the actuator is weak and needs replacement, how old is it?
dont know if you can put in a new spring or that its a whole replacement.
my vaccuum is -0.5 bar on idle and -0.7 on overrun, but thats got nothing to do with your turbo , its the underpressure your engine creates.
About your dumpvalve maybe its not connected right, a guy on here had the same problem with it not blowing off. had something to do with a t-piece he used that was narrowed down inside causing it not to blow off.
again as a comparison mine blows off from 0 - 0.1 bar boost already.

Edit: only if you rev it too about 5k you will hear the dump valve if you are not driving, its pretty pointless just revving to hear it blow off..
Its not blowing off because the engine isnt loaded enough the make the turbo create boost.