It depends on what you are replacing. If you are replacing an older PC that is not from the "i" series chips, then there is perfect sense in it. You have to give us more to work with. For example, I wouldn't replace my build with that system even though I am running a first gen i7, it makes no sense from a gaming perspective for me. Haswell will probably be on my list to upgrade to, pending reviews.
What do you want to do with this PC? I would recommend a different power supply, like one from Seasonic. Do you need the extra threads of the i7. If you are just gaming, I would go with the i5 3570k. If you do any editing or 3D work, I suggest the i7. I don't see an SSD on there, if you are building a new PC, I really recommend one for your OS and apps, it does really make things faster. I recommend Samung 840 Pros or Crucial M4s. The rest of the build looks good.
I just want replace my MB, CPU, Memory, GPU, HDD and cooling system, maybe in future I will replace my case to corsair obsidian 650D and PSU to Seasonic or Corsair, but not now.
maestro0428, PC for gaming and photoshop. I need i7 for photoshop? ...SSD it's a good idea, but what about corsair force series 3 F120 (120gb, Sata-3) ~100$?
and what is better? RAM, corsair xms3 or vengeance? don't forget for Noctua NH-D14
Ok so your current system is perfectly fine for what you would like to do. Just upgrade the RAM and video card for gaming and you are all set. You could also upgrade to an SSD and you would be set. There is no reason to upgrade much of anything else in your system.
I say go for the new rig parts list. It'd a quite an upgrade and you won't have to upgrade for a while. Sure you can get a new GPU and ram and maybe change the 2500 for the 2550 which has no difference other than the 2550 has onboard graphics. Has well will be nice but by the time you spent a the money on upgrading 1 or two things then getting a new motherboard for has well since its different socket and a new CPU and other things...you've spent the same amount.
next question, maybe just upgrade my i5-2500 to i5-2550K (262$) or i5-3570K (260$) for overclock? what is better Sandy 32nm / Ivy 22nm?
I would honestly just keep your current CPU. You can still overclock a non-K cpu. The only thing that means is that it has an unlocked multiplier. So for example your CPU runs at 3.3GHz. The CPU achieves this by taking the motherboard bus speed of 100MHz and multiplying it by 33. This gives you 3.3GHz. In the K model you can change this so for example you made it x35, it would give you 3.5GHz. However, for a non-K version to achieve this overclock you would have to increase your motherboard bus speed to lets say 106MHz giving you 33x106=3.498GHz. Before the Sandy bridge the only unlocked cpu's were the Extreme CPU's that were $1000. My first gen i7 920 stock runs 133MHz x 20 = 2.66 GHz. I overclocked the motherboard bus to 200MHz giving me 200 x 20 = 4.0GHz. So you can still overclock, you just have to do it a different way. People with a K model typically have to do a combination of both motherboard bus increase and multiplier. Also, the increase in bus speed can give you an overall performance increase because it is not limited to your CPU. The motherboard overclock also effects the speed that your RAM runs. So you typically want DDR3 1600 or 1866, maybe higher because it also uses multipliers.
So I say keep your CPU, overclock it a bit. You may have to read up on good clocks and how far you can push it, but you will find threads on people overclocking the i5-2500. I just don't see the need to purchase an entirely new CPU for such little gain. You money is best spend on something else.
Also your question on Sandy vs ivy bridge. Clock for clock the Ivy bridge is slightly faster then Sandy Bridge. However, Sandy bridge actually runs a bit cooler as you overclock because Ivy bridge is a smaller CPU chip so it has less surface area to dissipate heat. It also uses thermal paste between the chip and heat spreader, which is the metal plate you see on the actual CPU package. Sandy bridge still used the flux less solder, which is basically metal to transfer heat and is much better at it.