Apologies for delayed response — I've been trying out your suggestion. Unfortunately it didn't work too well for me.
However, I've also tried scanning a typical page as a 72dpi .tif right from the start, then setting the image size to 110% and optimising without any further 'treatment' at all. I tried it both as .gif and .jpg; neither of them is just as good as I'd hoped for, but both are more legible than earlier efforts and certainly acceptable as far as I'm concerned. The .jpg weighs in at 69.95kB (whereas I try to limit them to 30kB max) while the .gif is only 23.5kB, so I think I'll go with that method.
Why choose .gif in the first place? Because I figured I wasn't dealing with zillions of colours, just two tones (black and white) plus perhaps a couple of intermediate greys to help the definition along a bit.
Many thanks fourm member. I'll leave the box unticked for a while to see if anything else turns up