Neptune 262,
Some good points.
I would argue that in a modern, surveillance equipped tower, 'RSVA' is an outdated concept.
To do 2.5nm spacing (delivered to 4DME - as soon as the leader gets to 4MDE that starts to reduce) I need to be visual with the follower at 6.5DME.
This implies that being visual with both aircraft provides an added level of safety. However, when looking at a pair of aircraft heading virtually straight for me, I cannot tell if they are 2.7nm apart or 2.4nm apart, nor if they are closing or diverging. However, I can do that if I look at my surveillance system.