yes, magic can have a huge diffence on how the world looks (as monsters can). I'd concider the following:
Monsters:
How strong are the monster force - is it a "war" against them ie. are there need for constant troops and skirmishes to keep them to the wilderness or do they just pose a random encounter now and then.
Dragons would probably a nuisance for farmers with his sheep and cows as easy pickings, but seing that some dragons are intelligent they might not attack people to limit the need to "kill the dragon".
Magic:
Does the magicusers help everybody or just the nobles? If everyone can get healing for instance you'd have a very healty population - that might leed to fewer kids though.
Does the magic help growing crops etc ... then you can argue that the fields can support much more people.

Especially magic can change the world a lot ... making it very different from the classic middle ages
Good luck with your campaign