Nope not a necessity if like you say they're in good shape.
Yeah, the hard part is figuring out how much expansion space to leave where the floors butts the walls. :whistlingWhy not just throw some down and rack it? It will either go together or not.
As far as magic, you could dip it all in liquid fertilizer and see what happens. hehe Kinda like in Swamp Thing (The greatest tree movie ever)
As to re-milling, a decent mill could cut the back off and make a groove to match the existing tongue and you'd only lose a little less than a quarter inch.
I made that sound easy. So what?