I hate to say that I
may have been mistaken, but just so:
The Magic Overview Section of the SRD, Effect subsection,
Same effect with differing results clause, says that multiple, non-identical effects overlap, but the most recent version makes all the others irrelevant while it's in effect.
So, zugschef's 1 page spellbook might just work. It depends on whether each subsequent secret page casting can count the altered page from another casting as its original page. If so, then you have a 0gp method of scribing spells, but for each spell you need a 3rd level casting per spell level. (I thought that the command word would also be a sticking point, but just "fireballpage1, fireballpage2" would suffice there.)
However, successfully dispelling a secret page spellbook would destroy it. It actually makes the spellbook even more fragile, rather than less so. And the casting slot costs make multiple copies problematic. An eternal wand of it as a 2nd level spell (made by anyone with the
Rune domain) would mitigate the slot costs, for 4420gp.
Too bad even the 3rd level amanuensis spell can't copy a secret spellbook (non-magical writings only)
However, spells are written in 'complex notation', so the 3.0 version can copy them; no diagrams required.
