I will pitch in what I may
I fly in a VFR only program day and night. It is community based but referred to as a hybrid program because it is based at a hospital with the hospital name on it. The hospital subsidizes the program with some annual financial contribution. The crew is one paramedic, one nurse, one pilot.
We fly a BK-117 B-2 and NVGs should be here installed soon. The whole company is slated to be NVG equipped by the end of 2011. About half way there now. Mountainous, remote area bases getting them first.
In our IFR programs many of the hospitals have an IFR approach, some contain a VFR final segment, also used on departure. Low level wx reporting is pretty good here, but not everywhere. All of our IFR programs are single pilot, just like our VFR programs. Pay isn't much more for IFR. I would rather be VFR with NVG's. Also we have no autopilot and our GPS doesn't even have a moving map. We also will be soon upgrading avionics to Garmin 430's and the GMX-200 HTAWS. Very nice piece the 200 is.
We also have another aircraft in this program based about 20 minute flight north which is an AS-350 single engine with same crew compliment. The crew all work for us, no hospital affiliation. Just uses the same program name and is subsidized by the hospital.
As for the amount the IFR programs use the IFR. Some do quite a bit, others not that much. Much depends on how well developed the local low level IFR infrastructure has been developed, as well as hospital approaches. Hope this helps.