Given how little driving I do nowadays, and how much work needs doing on the house, I can't really justify spending too much on a replacement so I'm thinking of a hard limit of £10k.
Much as I love the look of the i30N, they're coming in at nearly twice that, same with the Focus RS (and having had a Mk2 ST previously, I think it'd be too similar).
Changing the satnav boot screen is something I think you can do in the menus on the satnav itself. If you take the SD card out (you have to use the 'Remove SD Card' in the menus IIRC) you can put it in a PC and there's a folder somewhere reasonably obvious that you can put new photos into.