I agree that tactics is the way to better challenge high level parties. Just up gunning the foes creates a vicious circle between the DM and the players (and rewards the players with more XP). By just using better tactics, it forces the players to think not just powergame.
The only way to really challenge high level parties is through attrition. Drain away some of the party's power prior to the combat with the BBEG, that is what the mooks are for. If the party clears out all the mooks then leaves before facing the BBEG, have the BBEG chase the party and fight them when they are spent. If he can't find them, attack their home and kill any loved ones to get their attention. Don't let the party buff and come in for a single fight with the BBEG, that is a huge advantage to the PC's, that any intelligent foe will avoid.