Though the attic is the common way. Many people put in wall plates to make it look professional but pretty much it works to just run a wire directly.
There is no way to determine anything from how many bars they get. Its all up to the manufacture what they mean. Cellphones lie all the time to make people think they get better reception than they do.
The strength of a wireless signal does not mean a lot. You can get strong signal but still have lots of errors do to interference. The more important one some wireless cards have that show the quality of the signal which takes into account errors.