I ran my gaming build with a G2030 for quite some time before I upgraded to a 2500k, so I've been in a similar situation.
Like geofelt said, it depends on which game you play. In my build for example, Bioshock Infinite had a meaningless improvement, but Splinter Cell: Blacklist was unplayable on the G2030. Certain games are optimised for multi-core processors whilst others run just fine on a dual-core.
If you are looking to buy a 4670k, then your motherboard should have a Z87 or Z97 chipset, as these will allow you to overclock the processor. Otherwise, the premium you pay for a "k" series processor is a waste of money.