Hi all, I've been looking at this problem for some time. I've now started using Afanche3D Pro (£29'ish) which is a 3D file viewer. It can import STEP files (and others) and export to DAE (and other formats). I've found it very us usfull.
The STEP files I receive are usually in mm so I've set Afanche3D Pro System Length Unit to mm and the Default File Importing Length Unit to cm (these setting are found in the Options (Grey cog in tools above work area). This is so it enlarges by 10. I then export as a DAE and import this into SketchUp. Because the units in my SU are set as mm the DAE file will import at x10 (that makes it x1000 the original model size).
Afanche do some other viewers that only open one file type (i.e. STEP viewer £23)