If you extract a key from a proprietary client to decrypt a private API, it definitely is illegal. If you do this as a corporation, it would also be easy to detect by abnormal usage patterns tied to your account and presents you as a nice big set of pockets to get sued.
Just screen scraping isn't illegal, but is fragile as fuck and will break at the worst time and you have no ability to implement version control to manage it.
There are plenty of things in a normal home that can cause serious signal attenuation (just installed new energy efficient windows? whoops! those IR blocking coatings severely attenuate microwave signals too). Poor AP placement is a very common cause of "slow wifi" and has nothing to do with your internet uplink.