There are some subtle differences between the RX400h and the HiHy related to safety, although you might argue that they're all "luxury" items.
The RX400h does have a rear camera that comes standard. The picture displays on the navigation screen. When backing up the SUV this can come handy if there are children around. I've seen some websites (for example,
http://www.coastaletech.com/hybrid_highlander.htm) that offer installing a rear camera on a HiHy, but it won't be from Toyota.
The RX400h also has a power rear door while the HiHy does not. If you've got a hand full of groceries with kids scurrying around, the power rear door could be helpful. Also, if it's late at night and you feel pulling up/down a rear door may be compromising your safety, a power rear door may again be useful from that perspective.
The RX400h also has a newer version of the nav system. I've seen it in the IS350; nicer graphics. The RX400h nav system is also voice-activated. The HiHy does not have a voice-activated option for its navigation system.
The RX400h's interior (comparing the leather option with the HiHy's leather option) feels a bit more refined an luxurious. But, the overall the amount of space, especially the cargo area, is smaller than the HiHy. Even the driver and passenger areas felt a tad bit more cramped from my memory of test driving the RX400. The 2006 model of the RX400h has more of an tapered eggshell backend (which I personally don't like), but that effectively cuts into the amount of cargo space available compared to the 2005 model. And of course, the RX400h does not have a 3rd row seat available. I'm actually surprised how many times I've had to use the 3rd row seat.
The RX400h also has a superior sound system... 11-speaker Mark Levinson, which kicks butt over the HiHy's JBL system. The RX400h also has a bluetooth option. So, I guess if you're concerned about hands-free, that's also another subtle safety advantage. The HiHy does not have a bluetooh option.
So, after touting all the nice amenities of the RX400h, why the heck didn't I get one? Well, there's of course a price to pay for these "luxury" items. From a sticker price, I believe it's about at least $10K more. With all those options described above... bump that up to at least $15K or more. You also pay a wonderful "luxury" tax that gets tacked on as you write out that check. Maintenance is also higher if you want your vehicle serviced by Lexus. That was the main deciding factor for me.
The other one is remarkably superficial; the body style/shape of the RX400h looks a bit too "feminine" for my taste. Especially the new 2006 rear. In fact, I wonder if they didn't target that shape specifically to appeal to the female audience. Yes, I know, sounds a bit chauvinistic, but, there it is. I feel that the HiHy's body style/shape is more neutral (in fact, overly so)... it has slightly masculine side in the front and a slightly feminine side in the back. Just my opinion, of course.
Good luck in your decision. If you can afford it, and that overall "feminine" body-shape (again, only my opinion) appeals to you, then of course, I would recommend the RX400h. If the luxury items aren't worth the cost and you are more interested in cargo space and utility, then I think the HiHy is a better choice.
