I've toyed with the idea of going up a notch with Metrocast, but since most of my bottleneck is at the wi-fi router level, my guess is it doesn't get me anything.
Am I right?
If you're pretty sure the bottleneck is in the WiFi, then I'd say yeah - there probably isn't enough reason to upgrade the internet service. And from the other thread it sounds like it is the WiFi. I think I'd look into getting a better router. They're pretty cheap and with a decent router the WiFi shouldn't be a problem, even with a very fast internet connection - unless you have something going on in your network where devices are sending a lot of data back and forth between themselves that has nothing to do with the internet. That latter situation seems very unlikely in your case, you'd probably be aware if your circumstances created that kind of situation.
If you upgraded your internet service it would help with devices that are connected to the modem by ethernet of course. But I think you indicated you don't have a problem with those devices.
Your WiFi router isn't built into your cable modem is it, as the equipment that your service provider gave you?