A Wraith won't always protect you tanks, It's best if you mix some Goliaths in with the tanks. Turrets should be almost everywhere a Spider Mine or building isn't and if your using Terran you should try to stay on the offensive because their defense isn't to great.
M&M will be seriously owned by 5 or 6 Lurkers and most people have them at the entrance to their base and to protect their miners. Spider Mines should be placed strategically across the map, because almost all Zerg units will die in counter with the mines.
Mines dont work that well vs zerg, hydras kill them fast. And a zerg player can easilly make 24 new hydras in 30 seconds, so it wont be too big a loss. Marines own hydras, and tanks own lurkers. Thats why u have light tank support and vessels. If u cast defencive matrix on a marine and send it into the enemy's lurkers and attack from a different direction 1 second later all the lurkers will attack the marine with matrix in stead of the attacking marines. Irradiate also kills lurkers, i always have 8-10 vessels in late game.