I had a bit of inspiration this evening and decided to put out another new build because I really want to know what you all think of it. First and foremost, I've made some additional performance enhancements in the pathfinding algorithms, which may have been why some were still seeing late game slowdowns even after the fire fix.
While I was in there though, I decided to split out the active portal pathfinding a little, and came up with what I think is a pretty good system. The way it works is that the minions will always rush straight for the center, until they run into a defender (tower). At this point, they'll make one attack, then try to find a route to the portal around it. If there is no route, they'll keep going and try to bash through the defender. If they did however find one, they'll attempt to go around.
Since they always take that first swipe, you can't just set up a maze of archers and force them through. Walls, with 20 hp now, are a must-have in securing your perimeter so that it won't fall immediately as the minions take their pot-shots. If you can hold it though, you'll have plenty of opportunity to take them down as they go around.
The only exception to this is any minion with a new "gate crasher" attribute flagged. This means that no matter what they'll just bust straight through any defenses to try to get to the portal. While I was at it, I also implemented a "charger" behavior where some minions will have short bursts of extreme speed. I'll leave it up to the player to find out which ones have it, but as a word of warning they have a pretty nasty bite.
Enjoy, and as always, tell me what you think in the comments!