Dave, I was looking at the bitmap in your original post, if you look at it closely it is not a very good image at all, from that image I would not expect to get a very good trace at all
Taking a photo of any image you want to auto trace can be problomatic, lighting, camera flash, shadowing all play a part & what on paper are solid black lines become shades of grey to any bitmap trace program. If you aren't perfectly square to the image when you take a photo you will also get a degree of distortion so the plans may not be 100% accurate
You would be better scanning if that is an option, if not then when photographing do everything you can to eliminate any possible problems. Don't save the images as a jpeg file, use something like BMP or tiff as these will retain a lot more of the pictures colour imformation.
I don't know how much you have used inkscape but there is a centreline trace for inkscape, it doesn't install with the main program it is one of the add ons you have to download & install. I don't use the program myself but know people who do