Worth Ugrading to Wireless N Router? - Belkin Play Max going for €41.45 on iBood

Hi

I was just wondering about wether there is any advantage of upgrading the router my parents have in their home after I saw the offer of the Belkin router that is on iBood today(expires 9/2/12 at around 11:30pm)

http://www.ibood.com/ie/en/

Since the maximum speed of the line is limited to 2mb/s, is there much point upgrading the router?
They have a large enough house, and had an ethernet cable network hub setup throughout the house when renovations were done a couple of years ago.
They have the router set up in the utility room where there is a hub for the network connections throughout the house, handy for some of the rooms that the wireless signal is unable to reach.
Files don't get transfered through the network to various computers.
They recently switched ISPs from eircom to O2.
When O2 replaced the old eircom router/modem with their own it seemed to affect the performance of the appleTV unit that connected to the network via ethernet. My parents have said that it takes an age for the stream to load up to a sufficient amount when they rent a movie, hours in some cases.
This is the main thing I'm curious about; does anyone know if the belkin could improve the streaming speeds for the appletv if that was to replace the random o2 one that is there at the moment? Sorry, I don't have any specs on the one that o2 provides.

I'm half interested in getting one myself and replacing the router/modem that came when I signed up to Magnet (real ugly random thing that I can't seem to access through my browser to change any settings)
Again, its serving it's purpose fine and I've no problems with the performance of the network with regard to general browsing and online gaming, but I don't like the fact that I have no control over the device and if there is an obvious advantage in having a higher spec model, it would be good to know.
Line speed is limited to 5mb/s.

Apologies for the spéil, I just am a bit ignorant on modems/routers/networks etc.
If anyone can explain the bare essentials and advantage of setting up a network with a decent modem or send me a link to outlining why and when you should upgrade your modem (even if your broadband is limited in the above examples) I would greatly appreciate it.
Thanks.