I would say they aren't essential but, if having them will give you peace of mind, then maybe the added complexity, weight, and maintenance will be worthwhile.
If you're going to install strobes, look seriously into the multiple-flash ones, the ones that flash 3 or 4 times. I don't know the proper name for them. I came upon an aircraft in the air that had those and they made a marked impression on me in terms of how good they were at attracting attention. And they did save time in the actual spotting in low light.
I think the logic is like this - the first flash gets your attention. The continued flashing sequence is then long enough for you to turn your eye and make visual contact. With standard strobes, the first flash catches your attention, but by the time you've moved your eye, the flash sequence has stopped, so you have to wait another second or whatever for the sequence to start again to see it and then make definite contact.
I don't think the difference would be life-savings critical, but I remember being impressed with the system the first time and I encountered it in flight. If you're going to put something in, you might as well put those in as anything else.