Well, I'm afraid ill make them sound stupid, but Ok:
Base capture: I know you already did this, but I have a different idea not involving combat. Once a flag is placed in a base, your hero has 10 seconds to come into the base. If they don't come in time, a dialog box pops up where each player can post res 1, 5, 10, 20, 50, 100, and 500 at a time. For each res posted you get a bonus chance of winning. After both players click done or 1 min the winner is decided by putting the chances together and and picking the winner (example: p1 - 1200 res p2 - 1000 res, p1 has 1200/2200 chance of winning, p2 has a 1000/2000 chance). The positives of this are that if p1 has a way stronger hero than p2, it doesn't necessarily mean he get the base (although he gets a higher chance if he risks more res). Also, this would take res out of the game, as all res bet dissapears. This would make the game longer if not using a current res/res in all system, or if betting with res in all.
Multi-layer caves: Would have tunnels leading up and down to go to different floors, only 3 floors in all or something, the main camp would be in the middle.
Tunneler: Can tunnel through small walls, not thick walls though, and doesn't make new tunnels. A unit.
Buried treasure: Hidden items and res only a special very expensive unit can find, not all over the map, only in a couple of areas.
Cave in: I saw someone else had this idea after I posted.
Giant worm: The opposite of cave in, would dig new tunnels.
Flooding: A random event, would flood large areas of the map (not bases), making it unable for most but not all units to come past. Only hero's and special aquatic units that are weaker than normal units would be able to come past. Units in the area receive a warning, and then have 30 sec to get out of the area before being destroyed.
Mold growth: Another random event, makes a random base unusable and uncapturable for a short time. Can also be made into a bomb by players.
Rock monster: A mini-boss, a slight chance to be dug up when mining res, would require a hero or several guards to destroy, and a lot of time. High health, low damage, low speed.
Earthquake: Another random event, splits the map in two for a short time with a crack, would slowly grow together. Unable to happen in bases, and units are just pushed to the side by it. Can also by made into a bomb by players, however direction is random.
Yes, I like random events.
I have a couple more, mostly random events though.
