As long as your experience is still good, then I wouldn't worry about it.
A newer router (802.11n or pre-802.11ac) will generally provide more range/coverage than your current router, but this is also at least partially dependent on the capabilities of the wireless devices connecting to it. If you do decide to buy new, I would recommend buying routers/client devices with "dual band" capability. While they tend to cost more, this adds a new frequency range to communicate on that does not have as many other types of devices using it.
However, before spending any money, I would look for sources of radio interference and try to fix any you find. This could improve your existing WiFi and if they are currently negatively impacting your WiFi, they will continue to negatively impact your WiFi even with a new router.
You can use a free tool like Metageek's inSSIDer (http://www.metageek.net/products/inssider/) to look for neighboring networks. If you check the 2.4 GHz channel graph, you will see that WiFi actually uses a frequency range, rather than just a single frequency. To avoid overlap, WiFi devices should really only use channels 1, 6, and 11 although many of them will auto select other channels. Find which of those channels has the fewest networks overlapping it and try using that channel.
Following that, look for (and reduce or eliminate when possible) non-WiFi sources of interference, especially those near the router. Here is a quick list of some devices I have found in 2.4 GHz (but by no means complete):
- Cordless phones
- Microwaves (generally only when operating)
- Bluetooth or other PAN wireless devices (keyboards, mice, etc)
- Game systems (Wii, Playstation3, Xbox360) - Note: I have observed a number of Xbox360's that communicate with their controllers even when "off" and only go silent when unplugged
- Video cameras - these can be a huge source of RF noise
- Baby monitors
- 2-way radios (walkie-talkies)
- Zigbee devices (not common in homes, and in US often run in 900 MHz)
- Cars (some car alarms, some tire pressure monitors, etc)