Question 1
Absolutely, in fact I have and I have stayed as a developer who can do some design. The combination has proven more than useful over the years and I suspect will only become more so as time marches onwards.

Question 2
Absolutely, as that's how I managed to gain the design skills I now have, I continue to search for these sorts of things now as well.

Question 3
The simple answer would be a 10 out of 10 but as with most things it's not that simple. Beauty being in the eye of the beholder, is different for different people. I do believe it's vitally important for interfaces to be engaging. I piece of software that is ugly and unintuitive but functional will still trump a similar software item that is perceived to be beautiful but is not functional. The key being to get both beauty and functionality together. Possession of solid design skills by a developer goes a long way towards helping that developer come up with that elusive mixture in their efforts.  Now technologies like Silverlight and WPF allow designers to craft UI layers leaving developers to hook those UI's to business logic. I as a developer enjoy knowing that to some extent I am capable of doing both tasks. Certainly useful is smaller development shops.