Considering the fact that one is probably generally not just using a modem as a hotspot for comcast, but is actually getting some personal use out of it, and considering that, for example, to declare even a *portion* of your rent or mortgage as a business expense in a home business you have to actually almost *exclusively* dedicate some square footage of your home, such as a den or what have you, to that business, and not use it for any personal purposes (cheaters on this front get dinged a lot if they are unfortunate enough to get audited, and the likelihood of a home business owner being audited in any given year is not insignificant), so I'd suggest that the fact that the modem might be taking up some real estate in one's home that they pay tax on is not grounds for compensation to that effect, since they are getting use out of the modem that has nothing to do with what may be benefiting comcast.
Even if you wanted to argue that the customers deserve more compensation than 50cents per month because of the real estate used by the modem, considering they can easily take up less than a tenth of a square foot, plugging that into the average square-foot rate for real estate in the area where the customer lives would probably only amount to perhaps a only a few additional pennies per month. If you factor in the notion that it would not be reasonable to compensate them for 100% of that, becuase the customer is getting some use out of the modem as well, it probably doesn't even work out to a whole penny.
As for bandwidth, if the public wifi is not on the same hotspot that the customer is expected to use, then the customer has the full wifi bandwidth, and anyone on the router's public wifi hotspot will not generally impact any upstream wired connectivity. And hey, it's comcast's network... they have a right to put whatever equipment they want on their own network. The modem that they you lease from them to use their network belongs to *THEM*... the fact that it may be in your home does not make it your property.
As for the impacts on the customer's network... it's not on the customer's network. It would be on comcast's network, unless the customer is expected to use the same hotspot that the router is supposed to have open to the public, which is probably not going to be the case.