So for the return game, which lasted considerably longer than the first. Over the course of the battle, as Spanish I drew two each of scout, rally and cavalry charge cards. The Spanish cavalry were victorious over the French cavalry on the other side of the river, and rallies kept the grenadier unit in the centre fighting hard to remove French units. Although badly neaten up, the Spanish army was able to win 6-4.
I have read the comments made 8 years ago about the guerrillas, and I agree that the rule is a little gamey, but without it, at least in this scenario, the Spanish have no chance at all. The guerrillas make for a more exciting contest. The rule is ahistorical, but C&C Napoleonics is not a detailed simulation of Napoleonic warfare - if you want that go and play Wellington's Victory or the La Bataille series. C&C is an entry-level system which introduces non-wargamers to the concept of hexes in shortish games which usually provide lots of excitement. Moreover, given the randomness of the card draws and the amount of die rolling a newbie has the chance to defeat a grognard, surely impossible in a more detailed simulation.