Well, in my opinion it all depends on what you have to do, even though having an ethernet cable is always a good thing, as @dloser said.
If your main concern of having a strong internet connectivity is for playing games, I would definitely buy an ethernet cable because it is much more reliable than a wifi connection, regardless of the signal strength.
If you mainly need it for browsing, you can try to find a way to kinda fix your current setup and squeeze the most out of your network card.
That being said, if you can afford the cost, it is definitely worth it.