Well, the PSR-E473 isn't quite that expensive. I'm seeing it for about $370 US on Sweetwater's website, which is what I normally see that keyboard priced at. And of course, the SX900 is dramatically more expensive -- about $2300 on the same site. One thing I've noticed is that, in my opinion, Yamaha has a gaping hole in their PSR line-up, from the E473 at $370, to the SX600 at $1100, with little in between. The EW425 is $490 (again, all these prices on Sweetwater in US dollars), but that is essentially just a 76 key version of the E473 with just a few added features. Even numerically, with their model numbers, they've decided to not have a 5-series (such as "PSR-E573" or "PSR-SX500"), even though they did a long time ago, with models like the PSR-540, or PSR-S500.
As far as the menu, yes, it can be a bit of a pain. But remember, many of the functions can be accessed quickly by just holding down one of the selector buttons for a few seconds to get you to that part of the menu list. For example, at least on my E433, if I hold down the "dual voice" button for a few seconds, that gets me right to the option to select the dual voice tone. And then from there, it's just a matter of going a few steps on the function list to get to other dual voice features, like volume, octave, pan, and filter. This way, you don't always have to scroll through dozens of function options to get to the selection you want.