Funny you should mention you were looking at a Windstar. Because that's the car I traded in when I bought my Ody. I had a '95 Windstar and it had the keypad. At the time I got the Windstar, I thought the keypad was silly but I came to appreciate it. Besides the reasons you mentioned, some others reasons are:
You don't have to play the hide-the-key-game and wonder if someone's watching you. Or worse, when there's no possible way to hide the key because you are surrounded by people, so you end up schlepping the stupid key with you on your weeklong business trip, during which there is no point to having your key other than worrying about not losing it.
And when your hands are full getting out of the car with packages, having a keypad makes it much easier to lock the car than having to hassle with getting the fob in/out of your pocket.
I also do a lot of running, so I'll drive to a race and just throw the key in the car. All the other runners have to take their keys with them (or convince themselves that they've all hidden their keys at the same time).
The KE model I mentioned actually has a bunch of nice features that the Windstar's keypad doesn't so now I can stop feeling like I had to sacrifice anything to get the Ody.
By the way, the manufacturer put me in touch with a couple local installers. They all say it's a laborious job (4 hours). I've only got 1 quote so far but it didn't surprise me: $200 for the parts and $175 for the labor.