I use the Gain control to push the whole track up or down, unless there's a compressor on the track, in which case I use the compressor's makeup gain. An alternative is to select the entire envelope and move all nodes at once, but that's clumsy and coarse. Offset mode isn't worth the bother.
What SONAR really needs are envelope editing features such as global level adjustments, scaling, inversion and limiting. Imagine being able to say "increase every node by 2dB except for those already over 4dB", or "copy this envelope to another track and invert it so it's a mirror image", or "make this envelope less/more extreme". AFAIK, no DAW offers such features, but then DAWs are still mostly stuck in a paradigm based on automated desks from the last century.