Same experience here. I have both the Select and the Premier, and the benefits stack. I believe that if you're committed to the IHG universe, having both cards is well worth it. $139 per year gets you two free nights at properties up to 40K. Even with some recent games some properties have played by getting themselves to 41K points, there are still lots of useful properties for the free night certs. The combination of stacking a 10% points rebate and the fourth night free effectively lowers the points needed for award stays by a little over a third.

And I agree: the points offered for an upgrade from the Select to the Premier provide no incentive to lose the benefits from the Select.