I like the idea.
Participate and have a KDR no worse than 1 kill per 2 deaths and you get a +1 multiplier to cRPG. You are still capped at x5 but you won't go under x2.
Participate, have a KDR no worse than 1 kill per 2 deaths and be on the winning side and you get a +2 multiplier.
Ideally, this multiplier is for, say, your next 10 hours of log-in time. It could be "for the next 24 hours", logged in or not, but I'd hate to see a rash of AFKs as people try to take advantage of this.
Losses in the fight must meet some minimum value to apply. Like at least 100 troops had to die in the battle and average troop armor value must have been at least 20 strat gold in value. That's a pretty low mark but would mean that 49 vs 49 would never count and at least 2000 gold would have to leave the game world in the form of lost armor.
So basically participating in a neutral village defense would be guaranteed to get you a bonus, unless you really suck it up with a horrible KDR.