I dont mind spending a bit extra if it will definately improve things - but would rather not 
Generally the more you spend, the better the 2.4ghz and 5ghz wifi. The cheapest one will probably do fine though.
Am i right in thinking that only certain devices (even n rated devices) actually see the 5Ghz band?
Yes, only certain devices do. You need to check this. I find that virtually all apple products within the past 3 years ago, most phones and a few windows laptops (depending).
I know my iphone does, but dont really use it for streaming television - I use my PS3 (downstairs) for that or my wii (upstairs) and my kids both have a roku box for streaming netflix.
The PS3 WiFi isn't great in my experience. No idea with the roku boxes.
You may not see necessarily better speeds at 2.4ghz. What you probably will see with a better router is that the range is better, the overall connection holds better, which ultimately means a better streaming experience. If your signals poor currently it can cause an unreliable experience.
Also is the bandwidth number the higher the better for streaming or again is that really only better if your device reads 5Ghz.
Streaming only really uses around 5Mbps max. So it's not using much at all. Streaming should work on virtually any router. If it's struggling wirelessly but not wired, then a better router is bound to help somewhat.
As a caution, 5 ghz doesn't travel nearly as far as 2.4ghz. So far away from the router 2.4ghz will be faster. Close to the router 5ghz will be significantly faster. So devices far away, put them on 2.4ghz. Ones nearby, put them on 5ghz.
Also the TalkTalk routers have pretty appalling wireless as far as I can tell. A friend of mine had standard wireless N asus router which was covering the whole house fine. When they switched over to TT (I was there changeover day) the new TT router didn't cover loads of the house (same channel etc). I ended up installing the old router for them.
Edited by ukhardy07 (Thu 01-Aug-13 10:34:51)