My database is currently at 315MB and holds about 175,000 posts in total.
The problem with saving images to disk and not the database, is you then also have to save avatars to disk. Which means if you run out of database space, you have a difficult job moving avatars to your new setup. And things get messy.
What I have done is save avatars to the database and set up an image uploader that saves to disk independently.