Is overclocking worth the extra ~100$ for CPU cooler, case, fans etc?

Depends how high you want to overclock and what you want/need to achieve.
Getting a good cooling system will allow you to reach much higher clocks without the risk of high temperatures.
If your already running quad @ 3.4 and only want to play games then I wouldn't worry (unless your temps are running too high), plus you can push the clock a bit without needing high end cooling.

OC is a hobby. The increase in performance is like 8-10%, or less than that.

And you are gonna need more than $100 if you want to hardcore OC.

The only benefit to overclocking these days is bragging rights. You will see a few extra FPS in your 3D games but you won't enjoy them any more. So if you just want to brag spend the money.

It takes a few minutes of every hours work , at the end of the year that ends up as $$$ saved , so for gaming bragging rights , for work projects equals $$$ at the end of the year . And it's not 100's more for a decent OC , I don't spend much more than 20.00 on a cooler , OC my 1100t and 1090 to 4.0 , 3.9 , the 18.00 cooler keeps them under 53c when maxed out , with stock coolers at STOCK clocks the cpu was hitting 62-64c which is not really good for long life , so the cooler was needed , at least in my case where the cpu is working @100% 90% of the time , with the OC it's necessary could not OC with stock cooler .
So it's not always about bragging right's , unless you're going for the ultimate OC

^^ +1

You don't need an expensive cooler. Arctic freezer pro is cheap and usually almost as good as much more expensive ones. Recently a lot of recommendations go to the hyper 212 evo.

Also not that expensive. Here in the UK an i5-3570k is £180 and the hyper 212 is £18. so 10% cost. and will allow an OC to ~4.4Ghz or over %20 faster than the base clock or 15% of the turbo clock.

So it actually extracts additional value. Your PC is often quieter as a result too and runs cooler.

Seriously, If you have to ask this question in the first place the answer is No!

There's a whole lot more to overclocking than cooling hardware!

And overclocking for performance gains is way past bragging rights, but you have to do it, to fully understand why they do it.

If you are even considering overclocking, learn how to do it first then worry about the hardware you need to accomplish it.

I would love to see where you get your information from. You can get a decent cooler for $20-30 and OC a , well lets say an i5 2500k from 3.3 GHz to 4.5 Ghz and see much higher than 10% performance increases. For some it might be a hobby for me its about getting more value out of the parts I have.

First, I highly recommend getting a 3rd party HSF, even if you do not Overclock the processor. The Cooler the CPU operates the Better!! The stock HSF is at the bottom of the totem pole when it comes to performance. The push-pin attachment is much poorer design than ones that come with a back-plate.
With the stock HSF, Games will push the Core temps up, possibly to 70C, and if you rum prime 95 to check system stability and or to verify no memory errors tha may push temps up into the 80s.

As Far as if OC is worth it much depends on applications. For multithreaded apps that are cpu intensive, YES even a modest OC (4.5) can be benifitial. To really notice you need to get a 10% or > performance increase.

A SSD is ONE upgrade that will normally provide a noticeable improvement in loading/writing files.

Thanks for the advice everyone!!¿ 

some ppl only overclock as a means to prolong upgrading

OP, I think you are overestimating the cost increases required to OC. The only thing I spend extra money on was the k chip (which you already said you are getting) and a Hyper EVO 212 CPU cooler that is around $20-30 USD.

Using a Z77 (ASRock) and i5-3570k I am currently running at 4.3GHz OC at less than stock voltage.

There are LOTS of threads in here around how to OC, especially for that chip. Read a few of those and you should get a good idea.

I personally wanted to OC to get some extra performance out of my chip and thus improvement in gaming, but also, and probably more importantly, to extend the life of the chip from becomming obsolete. With air cooling and a good chip there are plenty of people here who have gotten 4.5GHz to 4.7GHz. An improvement from a stock max of 3.8GHz to 4.5GHz is a great improvement (18%).

To get you started in OC, consider the following:

The higher you OC, the higher the voltage needs to be.
The higher your voltage, the hotter the chip gets.

Hope that helps -- this forum definitely helped me out and I was a complete n00b building this PC, and now I have a stable OC at 4.3GHz and I am not pushing anything near its limit.