Depends; the 18-70 is one of the best kit lenses produced in the last few years (I still use mine, a LOT), but it's still a kit lens. If you can 'trade even', that is get enough money from the sale of your 18-55 to cover the 18-70, I'd say go for it, but if it's going to cost you additional, I'm not sure that you wouldn't be better off putting that cost toward a new/different/better lens.
Ignoring any issues of image quality, An extra 15mm at the long end isn't going to make that much of a difference, it's only 27% longer, which you can easily walk a few steps forward for
Yea, focal length is not my concern. My main concern is IQ. It most likely will cost me more, but I guess I'll either keep my 18-55 or sell it for another, better lens.