I just went through this in a house that we just bought! There are a couple of methods that you can use that are inexpensive... 1. You can use a brick to go over the wall and break the texture, and then follow up with sanding to smooth out the scrape marks. This works faster than a scraper tool because it is wider, not to mention cheaper! 2. I used a 20 grit sandpaper for stripping floors, it is basically gravel glued to paper! You have to be careful with this because if you push too hard, it will dig into the drywall something fierce. But if you are careful, this method also works great!
With both methods, you have to apply a thin coat of drywall compound over the entire surface to level it out and fill in any scrapes you made. When you apply the compound, put it on in thin coats and lightly go over it with a damp sponge to smooth it out. This will reduce the amount of sanding and dust to smooth it out. My walls look great with just a heavy nap roller which will also help hide some of your minor imperfections.
Good luck! If you have any questions, e-mail me. I have done many home restorations and remodeling and I am currently working on our 90 year old home.