You actually don't need to. A letter comes with them saying "Please do not return your old router". At least ours did.

Does anyone know if this will substantially improve non WiFi performance over a Rev D.

The rev I is just a better router in general compared to your rev D

You might see improved range on the rev I

Wireless speed yes because a Rev D is wireless G while the Rev I is wireless N

I would get that replaced

What rev do you have?

Unfortunately, I paid the $99 price two or so months ago. But I am happy with it, so I guess this is OK. It seems to me that this price drop is a way to clear out inventory in anticipation of a new router - a rev J? I wonder what they will add/ Dual Band, 802.11ac, etc.