I would not replace any track. I grew up with the originals so to me every bonus track is not part of the organic flow of meaning and emotion that I get from the great masterpieces in their very pure form. That does not mean that there are only great tracks on the originals (i.e. "It ain`t easy" on Ziggy is useless). But even the songs I like less do mean something to me in the flow of the whole album.
Same with compilations: I could easily burn a couple of CDs with only my favourite Bowie tracks on them. Wonderful, but they would never beat the likes of Space Oddity, Man who, Ziggy, Hunky, Station, Low ...
Bonus tracks are nice to have but I could easily do without them. Chuck them all on one or two "bonus albums" and sell em on their own. The Originals are magic, no improvement needed.
And I want to believe
In the madness that calls 'now'