I believe the correction for ISA-20 is 7% (i.e. the altimeter overreads by about 7%). It can get a little cooler than that (-5 degC on the surface) in NW Europe, but usually not too much.
Thus a 200 ft DH becomes a 215 ft indicated DH. A 1500 ft step down height becomes a 1600 ft indicated step down height.
Is the correction worth making? Well, there's an argument that the 15 ft gets lost in the tolerance of the instrument itself and the altimeter setting, after all it's only half a mbar/hPA. And the 1500 ft step down probably has a 1000 ft terrain clearance built in.
There's also an argument that you might as well adjust the figures for known calibration issues like temperature correction, and preserve the safety buffers for other eventualities.
It's a judgement call...