Peter, the way I approach these approaches is to have the PF on the instruments until short final. It's OK to take some peeks to see where the rig is, and how far, but primarily it's on instruments until fairly short final. If a circle is required to make sure it's the right rig & where the heliport is (it's not that uncommon to have several rigs in the same block over here) then the circle is on instruments. The PF checks the rig as he flies over it, then goes back on instruments for the circle. It's ok to look out to see where the rig is, but the circle has to be on instruments primarily. I've had copilots try to fly me into the water by trying to fly visually when there is nothing to see, & it only takes a couple of seconds to get into the water from <500'. The PNF has to keep sight of the rig & also monitor the PF. Trying to do this single-pilot would terrify me, and it's done over here, sometimes with fatal results. This requires a crew with really good coordination and mutual respect. I agree that from a few miles out, the rig appears as one light. And on a really dark night, with smoke in the air, it can be impossible to see any light reflections on the water, & there are no cues as to rate of closure or height, & the rig lights can start to move around. That makes the approach very difficult.
The takeoff is also on instruments, from the initial pitch pull from a hover, with the PNF monitoring the PF full time. IMO, the takeoff needs to be positive and forward, getting to Vmin as soon as possible. Trying to hover OGE and then transition to forward flight is begging for trouble. Airspeed is life. I just pull power and put 2-3 degrees nose down pretty much simultaneously, & try to get Vmin as soon as I can; you're certainly IMC as soon as you get off the deck, & you'd better fly that way. You're totally blind when you go from the bright lights out into the dark, no night vision at all.
Like you, I don't do this as often as I'd like - mostly it's broken rigs or broken roughnecks, but 50 miles is a very short trip for me. A couple of nights ago I went 275NM one way, then back in, & it's seldom less than 100, so we both get a chance to drive.