To a degree, yes, but a mixed mode N router will still be better than G only in most situations.If I have an N router but have other non-N clients (older PCs and laptop) would this slow the whole router to 802.11g and thus negate the benefit of N?
BUT...
If you buy a new router, set up the new router dedicated to N only, set the old router dedicated to G only in access point only mode (you already have the hardware, may as well use it to optimize the network). Alternatively, go with a dual band router, set the 2.4ghz band for mixed mode and the 5ghz band to N only, and connect the Joey to the 5ghz band.
Yours is a good example of why the "official" wireless Joey will have a dedicated access point, Dish does not want to get involved in home networking issues.