Why does it have to end?
Live's downfall was(IMO) the fact that there was a new expansion with (badly)re-written lore/new zones with that extra +50 hp and mana on each item once every three months. That and the ease of leveling that came with it.
More and more progression and things to do don't ruin a game. Making everything easier and having crappy content coming out constantly does. SoD has neither of those, as the EXP isn't getting any easier, and the content coming out is far from crap.
But back to the topic at hand! I think that more tomes would be awesome for both the reasons that you stated, and the fact that for DPS classes it would be very cool to have things that weren't damage in tomes. An accuracy tome, or a very specific tome for certain abilities would be very cool.