Scan Tailor can semi-automatically separate scanned book openings into left and right pages; it can recognize the outline of the printed area of the page; it can provide new, clean margins; it can clean up speckles and even do some de-warping. The results are excellent, though it does take some hand-holding, so one has to invest a bit of time to do a whole book. But 90% of the work is automatic. Recommended.
Best,
Dominik