But only to the extent that you need the accuracy of a non-Newtonian situation or the point-mass approximation isn't adequate, and those are really minute effects compared to the magnitude of the solar barycentric motion. For Newtonian point masses, the combined force is the (vector) sum, and since in this case the displacement is always extremely small compared to even Mercury's distance, adding the individual planetary displacements is a really good approximation. (This breaks down when the perturbing masses are larger, for example, so that the variation in force due to one perturber changes significantly over the distance of the perturbation caused by another). Again, it depends on what "significant" means in a particular context.