I was fortunate not to have had to sell either my Nikon D3S or M9 systems to acquire the S2 kit although I did have to part with my earlier MF kit and a LOT more lenses to afford it.
As my results improve with the S2 I have given serious thought to whether the Nikon D3S system is something I should consider selling. The main advantages for me with the Nikon kit are it’s low light capabilities, longer reach, much faster capture rate (for sports) and it’s near foolproof AF system…the most important of which (to me) has been AF. I’m not sure whether Leica has improved the AF on the S2 or if I’ve improved but the gap between these two systems has narrowed dramatically. I am nailing a much higher percentage of shots with the Leica now than I did in the early days. And while the images with the Nikon are very good…they don’t WOW me the way the Leica shots do.
My M9 kit is sacrosanct…at least for as long as I am able to afford to keep it. For me it’s just in a completely different category than the S2. I use it less than I should but that’s mostly because I enjoy shooting with the S2 so much that I select that system even when the M would be the more intelligent choice.
I am not surprised to hear that the S2 is encroaching on your use of the H4D/60 kit. To my mind the S2 can do most things the Hassy or Phase systems can do in a much more convenient and flexible package. I find myself shooting my S2 in many more situations than I did with my earlier MF kit…sounds like you are too.