The Brits never joining the Euro essentially is them saying they're not part of the EU so what's the point of this vote?
The UK is in the EU and belongs to the EU single-market,which means a commitment to freedom of movement goods, services, labour and capital.
There has been a huge influx of migrants, offering cheap labour,from Eastern Europe(most notably Poland),to the UK,in recent years,after they were admitted to the EU. There is also the anxiety about accession of Turkey and the fear that Turks might swamp the UK. Getting out of the EU,with it's commitment to freedom of labour, would mean a halt or at least slowing down this level of immigration. Kind of like the controversial issue of immigration from Mexico,to the US .currently.
Also,there is stuff such as loosening the regulatory burden of the legislation that the EU puts on a lot of small businesses,getting control of Britain's fishing waters and the reclaiming of Britain's own seat at the WTO.
Also, with the Euro currency zone currently stagnating economically,there is a feeling among Europe's elites that the EU should be given greater powers of government spending ie fiscal powers ,along with monetary powers to make the Eurozone work. Given ,that the UK is not part of the Euro it's difficult to see what role the UK will play in the EU in ,say, ten years time.