It is only really worth it if you plan to overclock the 4690k. If you don't also have a high-end motherboard to support the overclocking and a good after-market CPU cooler getting the 'k' model wouldn't be the best use of your money.
The i5-4590 is a perfectly good CPU and will be viable for several more years, so if you're on somewhat of a budget I'd recommend sticking with the i5-4590 and putting the 45 EUR towards another part of your system.