Since when is your internet connection the only thing you do with wifi? Now I agree if you don't do anything like streaming or moving files around your local network and your current wifi is greater than your internet bandwidth then sure there is little reason to upgrade.
If your on a 4Mbps connection internet connection and don't do anything local, why did you fork over money for a dual band N? Freaking B router would handle 4Mbits per second
So why did you upgrade your router before your 3800, which if you bought it when was new was prob pushing $200, now you can get them for under $100
But we are on the same page - nobody is going to rent a router, not in a way that the user would see any benefit to doing it, it would clearly cost them more than just buying new when they wanted it. And either putting the old one on a shelf, using it as AP in other part of the house.. Maybe add wifi to the shed out back
Or selling it to recoup some of the cost of the new one.