I don't think $450 is reasonable by any stretch of the imagination, but I have never had to pay that to stay onsite at any of the 3 hotels, thankfully.
When I have stayed onsite, thus far (and it will probably change in the future as DLR becomes more developed and prices go up) I have always had some sort of PIN code discount or AP discount or other special offer of some kind...and my room rate has never been over $200 per night. In fact, it's usually been well below $200 before tax - sometimes I've paid $159, sometimes it's been $179, or somewhere in that range.
I go to DLR at very popular times, like HalloweenTime and Christmas time. But I pay attention to the specific weeks. If I wanted to go during Christmas week or between Christmas and New Year's (which I wouldn't), I would not get much of a discount at all. So I go before Christmas week, get the discount and get to experience the full holiday season. This doesn't mean that I can always afford to stay onsite even if it is well below the $200 range per night, but I try to.
As for what makes staying onsite 'worth it,' it's really different for each person. It's not for everyone. Some people look at their trips as being all about the parks themselves, and the hotels are merely a place to sleep and shower. Others count the hotels as part of the whole Disney experience - and I fall into that category.
Sure, mostly I just sleep and shower or take mid-day breaks in the hotel room, but staying onsite enhances my overall experience tremendously. I like the feeling of beginning and ending my trip on Disney property, from when I get out of the car to when I get back in it to leave.
I love looking for hidden Mickeys in the carpeting or in the bedspreads or in the wallaper. I love seeing the little details Disney uses in their rooms to complement the themes of the hotels. I love being greeted by happy Mickey ears bath products in the bathroom when I arrive. I love to get my room key (called Key to the Magic) when I check in, which has my name on it. I love knowing that there is a possibility of being upgraded to a better room with a better view (which is what I got in December). I love receiving my pink folder with Goofy on the cover at the front desk, filled with brochures and maps and info. I love making use of the Magic Mornings. I love being able to send my purchases back to the hotel for free so I don't have to schlep them around the parks.
For me, the Disney hotels are a big part of my enjoyment and immersion in the Disney magic during a trip.