A new HDMI mod for the Sega Dreamcast was released a few months ago. It only goes for about $65AUD on Aliexpress. I have been putting it through its paces for the last month and whilst it has pretty bare bones options in the OSD, the picture quality is excellent and is certainly an upgrade over analog RGB. If you bear in mind the low cost, this is a great option for those that want the ability to plug there Dreamcast into their modern display using a HDMI cable whilst having a very nice picture.
Video review (not mine) is posted below as well as link to go buy your own if you wish