I don't see how DSi sales at this point are beneficial to Nintendo. Sure, they make money off the hardware that's sold, but these sales are cannibalizing the sales of the 3DS. Someone who buys a DSi won't be able to buy the new 3DS software. Instead, they can only play old DS games which I'm sure Nintendo still makes money off of, but not much if these games are being bought used or at budget prices, which tends to be the case with older software.
It should be Nintendo's goal to move consumers towards buying 3DS software instead, because this is where they are going to be making the bulk of their handheld money in the next 5+ years. Selling the DSi might be profitable in the short term, but since it cuts into 3DS sales its a bad thing in the long run.