Probably not a lot of benefit in upgrading a four year old router if it is working well. What model of SpeedTouch do you have?
If you upgrade to gigabit wired or N wireless, all of your devices would need to have those capabilities as well to take advantage of potential higher speeds. Also, how fast is your Internet connection, as you may find that the limiting factor.
I would either keep the current router or get one that is a significant upgrade, although that puts the price above your target. The Netgear N600 is a good example of what I would look at for an upgrade -- dual band N, gigabit 4 port Ethernet, and all the capabilities you could need.
The other option, as there are always other options, would be to continue using your current unit for its DSL modem function and attach a wireless N router configured as an access point. That would give you wireless N, a gigabit switch for locally wired machines and drop the price in half. I use 4 DLink DIR-655 to distribute two broadband networks throughout my house and they work quite well.