Running In - I think you are over-egging the capability of TCAS somewhat - it will tell what quadrant another aicraft is and issue a TA if the altitudes conflict but it is not much use when conducting a multi-aircraft search at low level in poor vis/night when you need to know exactly where the other aircraft are - TCAS doesn't have that level of accuracy.
Frankly having the TCAS alerting all the time during such an op would be very distracting. And since I am talking about searching, the Radop would always be in the radshack. In fact the TV screen with the radar plot on is easily visible from the cabin door when winching - maybe you haven't seen what the latest fit looks like.
I'm not saying TCAS wouldn't be nice for general ops but in specific situations the I band radar wins.
3D - I'm not quite sure what you are getting at - if you mean the ARRCK might task a military asset instead of a civ one then it is possible but only for good operational reasons. The advantage of having the RCS is that you can see at a glance what the other flights are doing and whether they are closer to a job because they are airborne on training. You can also see how the serviceability affects the UK cover as a whole and choose not to send the obvious flight because it would leave half the UK with no SAR cover.
Still waiting re IMC below MSA
