The Dreamcast doesn't output 480p over SCART, only 240p/480i. So, if you want the console to directly output 480p, and get better image quality, you have to get a VGA Box. The Toro VGA box from Beharbros can output 480p over VGA and
over SCART, because it has a sync combiner built-in. Then, you can hook it up to the Framemeister, to have your image upscaled to whatever resolution you have set up, like this:
Dreamcast - Toro VGA Box - SCART cable/JP21 adapter - Framemeister - Monitorhttp://retrorgb.com/dreamcast.html
The info on this page is very informative, and the video pretty useful. The Toro is explained at 7:25.
On the other side, the Framemeister can convert an 240p/480i source to 480p, but then again, the Framemeister is known to handle 240p and 480i better than 480p, has a slight input lag and adds some picture noise: http://junkerhq.net/xrgb/index.php?title=Dreamcast
At this point, you are better off with an OSSC, which is a line doubler with almost no input lag, as opposed to the Framemeister which is a pure upscaler (investigate the differences), using the following configuration:
Dreamcast - Toro VGA Box - SCART Cable - OSSC - Monitorhttp://retrorgb.com/upscalercompare.html
That said, using the Framemeister with the Dreamcast, I doubt that you will get an AMAZING increase of image quality, even if you get a VGA Box. But even so, the Framemeister can still do its job and be very useful, because just like the OSSC, also allows to play non-VGA compatible games, that only output 15,6 kHz no matter what, on screens that only support 31,2 kHz.
To summarize, I doubt that you will get a substantial increase of image quality if you buy a VGA Box to make the DC output 480p directly, if you already have a Framemeister. If you don't, the the choice nowadays is the OSSC over the Framemeister, when it comes to the Dreamcast.