Heat olive oil in a large skillet over medium-high heat. Add the garlic, chili powder, cumin, and mushrooms; sauté 5 minutes. Add spinach and salt; cook for 1 minute or until spinach wilts, stirring frequently. Drain; return mushroom mixture to pan. Add cream cheese; cook 2 minutes or until cream cheese melts, stirring frequently. Place the mushroom mixture in a bowl; set aside.
Heat 1 cup salsa in a saucepan over low heat. Dredge both sides of each tortilla in warm salsa using tongs, and stack the tortillas on a plate. Spoon 1 heaping tablespoon mushroom mixture into center of each tortilla; fold in half, and arrange in skillet, overlapping slightly. Top with remaining salsa, and sprinkle with cheese. Wrap handle of skillet with foil, and broil enchiladas for 4 minutes or until the cheese melts. Top with sour cream, and garnish with cilantro sprigs, if desired.