If I were upgrading wheels I would say get new wheels if I was downgrading to avoid doing a quick tire swap, I would probably not do it. Save the money and just swap tires, maybe take some time and practice a bit, Also having a good tire lever will help, I like the Crank Bros Speedier Lever.

Now If I were to upgrade wheels I would probably do some measuring on the hubs and calculate the distances between the rotor mounting and maybe shim it out as needed (Syntace makes some that work just fine) so both work equally.