Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Stir in the spaghetti, and return to a boil. Cook, uncovered, stirring occasionally, until the pasta is cooked through, but still firm to the bite, about 12 minutes. Drain; toss with 2 tablespoons of the butter.
Melt the remaining 2 tablespoons butter in a large skillet over medium heat, and cook and stir the shallots and mushrooms until the mushrooms are tender, about 5 minutes. Stir in the grape tomatoes and garlic, season with salt and pepper, and cook and stir until tomatoes are heated through, about 3 minutes. Add the shrimp, and cook until the shrimp just begins to turn pink, stirring occasionally.
Stir in the white wine and lemon juice, reduce the heat to medium-low, and simmer until shrimp are opaque, about 5 minutes. Stir in the spinach; once spinach has wilted, stir in the half-and-half and Parmesan cheese. Simmer until all ingredients are heated through and the sauce is slightly thickened, about 5 minutes. Serve over the cooked spaghetti.
