I agree - the bonus is only for the first attacking unit. Also the manual says cease fires last for "approximately 16 turns". I don't know if anyone has researched this in more detail - if so, it'd probably be in the Great Library at Apolyton. I know there is a combat thread there with details about sneak attacks.
In my own games [ICS + Early Conquest], I am usually happy when a cease fire expires, so I can attack without damaging my reputation (not sure why I even care about rep tho). Sneak attacks by the AI really hurt sometimes, but usually they are not very effective, and soon the AI is willing pay lots of gold to restore the cease fire. In general, I refuse cease fire and peace offers, except in "weak moments" (for example, I am trying to establish an outpost in the enemy camp) or unless they offer me lots of gold. Or maybe if I have chosen that civ as a trading partner.
These comments assume my civ is fairly ready for war. Maybe not a large army, but enough cities, roads, map info, tech, etc that I can either attack soon, or at least defend cheaply.