Screenshots: http://imageupper.com/g/?S020001008V14036287812408235
	     First screenshot is just with Blinn-Phong shading, the second screenshot is the occlusion map and the third screenshot is the result of applying the shader to the second image with the parameters you suggested.

        public override void Draw(GameTime gameTime, SpriteBatch spriteBatch)
        {
            base.Draw(gameTime, spriteBatch);

            GraphicsDevice.SetRenderTarget(renderTargetA);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            Material material = new Material();
            material.DiffuseColor = Color.Red;
            material.AmbientColor = Color.Red;
            material.AmbientIntensity = 0.2f;
            material.SpecularColor = Color.White;
            material.SpecularIntensity = 2.0f;
            material.SpecularPower = 25.0f;

            #region Billboard
            GraphicsDevice.DepthStencilState = DepthStencilState.None;

            Matrix billboardMatrix = Matrix.CreateBillboard(lightPositions[0], camera.Eye, camera.Up, camera.Focus - camera.Eye);

            this.camera.SetEffectParameters(billboard);
            billboard.Parameters["World"].SetValue(world * billboardMatrix);
            billboard.Parameters["Tex"].SetValue(lightTexture);
            billboard.CurrentTechnique = billboard.Techniques["Technique1"];

            foreach (EffectPass pass in billboard.CurrentTechnique.Passes)
            {
                pass.Apply();
                this.GraphicsDevice.DrawUserIndexedPrimitives<VertexPositionNormalTexture>(PrimitiveType.TriangleList, lightQuad.QuadVertices, 0, lightQuad.QuadVertices.Length, lightQuad.QuadIndices, 0, lightQuad.QuadIndices.Length / 3);
            }

            GraphicsDevice.DepthStencilState = DepthStencilState.Default;
            #endregion

            #region OcclusionMap
            Effect tempEffect;
            foreach (ModelData m in models)
            {
                tempEffect = m.Model.Meshes[0].MeshParts[0].Effect;
                m.Model.Meshes[0].MeshParts[0].Effect = occlusion;

                ModelMesh mesh = m.Model.Meshes[0];

                occlusion.CurrentTechnique = occlusion.Techniques["Technique1"];
                this.camera.SetEffectParameters(occlusion);
                occlusion.Parameters["World"].SetValue(world * m.Transform);

                mesh.Draw();

                m.Model.Meshes[0].MeshParts[0].Effect = tempEffect;
            }
            #endregion

            #region PostProcessing
            GraphicsDevice.SetRenderTarget(null);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            Matrix projection = Matrix.CreateOrthographicOffCenter(0,
            GraphicsDevice.Viewport.Width, GraphicsDevice.Viewport.Height, 0, 0, 1);
            Matrix halfPixelOffset = Matrix.CreateTranslation(-0.5f, -0.5f, 0);
            postProcessing.Parameters["MatrixTransform"].SetValue(halfPixelOffset * projection);

            postProcessing.CurrentTechnique = postProcessing.Techniques["Godrays"];
            Vector3 lightPosition = Vector3.Transform(lightPositions[0], world * camera.ViewMatrix * camera.ProjectionMatrix);
            postProcessing.Parameters["lightPosition"].SetValue(new Vector2(lightPosition.X, lightPosition.Y));
            postProcessing.Parameters["Tex"].SetValue(renderTargetA);
            postProcessing.Parameters["exposure"].SetValue(0.2f);
            postProcessing.Parameters["decay"].SetValue(0.999f);
            postProcessing.Parameters["weight"].SetValue(0.2f);
            postProcessing.Parameters["density"].SetValue(0.9f);

            spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.Additive, SamplerState.PointWrap, DepthStencilState.Default, RasterizerState.CullNone, postProcessing);
            spriteBatch.Draw(renderTargetA, new Rectangle(spriteBatch.GraphicsDevice.Viewport.X, spriteBatch.GraphicsDevice.Viewport.Y, spriteBatch.GraphicsDevice.Viewport.Width, spriteBatch.GraphicsDevice.Viewport.Height), Color.White);
            spriteBatch.End();

            GraphicsDevice.BlendState = BlendState.Opaque;
            GraphicsDevice.DepthStencilState = DepthStencilState.Default;
            GraphicsDevice.SamplerStates[0] = SamplerState.LinearWrap;
            #endregion

            #region BlinnPhong
            GraphicsDevice.SetRenderTarget(renderTargetB);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            foreach (ModelData m in models)
            {
                ModelMesh mesh = m.Model.Meshes[0];
                Effect e = mesh.Effects[0];

                e.CurrentTechnique = e.Techniques[m.Technique];
                material.SetEffectParameters(e);
                this.camera.SetEffectParameters(e);
                e.Parameters["World"].SetValue(world * m.Transform);
                e.Parameters["WorldInverseTransposed"].SetValue(Matrix.Transpose(Matrix.Invert(world * m.Transform)));
                e.Parameters["CameraEye"].SetValue(new Vector4(this.camera.Eye, 0));
                // TODO: LightSource Color + Intensity
                e.Parameters["LightSources"].SetValue(lightPositions);

                mesh.Draw();
            }
            #endregion

            #region Drawing
            GraphicsDevice.SetRenderTarget(null);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.Additive);
            spriteBatch.Draw(renderTargetB, new Rectangle(spriteBatch.GraphicsDevice.Viewport.X, spriteBatch.GraphicsDevice.Viewport.Y, spriteBatch.GraphicsDevice.Viewport.Width, spriteBatch.GraphicsDevice.Viewport.Height), Color.White);
            spriteBatch.End();

            GraphicsDevice.BlendState = BlendState.Opaque;
            GraphicsDevice.DepthStencilState = DepthStencilState.Default;
            GraphicsDevice.SamplerStates[0] = SamplerState.LinearWrap;
            #endregion
        }