Yes.
Actually, the eInk screen is the same on both devices. The controller is different and so is the default font. I prefer reading on my Kindle than on the Sony -- I think the main reason is that it is easier for me to hold the device with only one hand and turn the pages easily. I find that with the Sony, I can hold it in my left hand, but have to reach over with my right hand for each page turn -- which means if I'm reading while eating, I have to keep putting my fork down!
Since you already have the Sony reader, it seems like you only need to learn a little bit about how to put books onto it -- and where to shop other than the Sony store. But, if that's intimidating, the Kindle is a great device.
There's no one perfect device. You're likely to find things you like about either one. Today, a new 505 is less expensive than a new Kindle, but if you can find a used Kindle, that will make the prices just about the same. Most of the time, for new releases, the same book is $2 cheaper at Amazon. ... but it's going to take a lot of $2 savings to cover the initial cost of a new reader. There are a lot of free books available for both devices.
Here at MobileRead you'll find advocates for both devices -- rabid fans in some cases. You can take a look at the
device comparison matrix in our Wiki; that might help you make a decision.
Good luck. In the meantime take time to tell us what kind of books you like to read.