When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The upgrades you should be thinking about will depend on the music you listen to. What you can afford will depend on whether you're gonna install it yourself or not. If not, a good chunk will go towards labour. With £500 you will certainly notice a big difference, but also consider whether this is likely to be the first stage of further improvements - can become a real bug, once you're hooked. Have fun.