Why would you want to overclock it? Gaming? Faster speed? Not worth it.
Overclocking is definitely worth it, it's a huge value for the price. An extra 1ghz faster CPU would cost over $100-200 in price but only $20-60 in a heatsink from low to high end and maybe $50 more at most for a better mobo.
I'd say I personally only spent about $60 for overclocking gear as opposed to non-overclocking, yet I gained over 1.3ghz on my CPU and memory controller, 1.1ghz on my RAM, and 35% on my GPU. I'd say that's definitely worth the less than $100 I spent.
It also depends what games you play, but most modern games are CPU intensive. I personally not only play a very cpu intensive game like Starcraft 2, which definitely appreciates overclocking (100mhz is roughly equal to +1-3FPS, so 15 faster fps is HUGE increase in performance when you are talking about minimum frames per second, where even a 3960x at stock will struggle to run 4x4 in starcraft2 when a big battle occurs, the nature of sc2 as it is).
And, i also stream all the games I play. Now maybe you don't stream, but given your stance on overclocking I'm guessing you probably couldn't handle streaming on your system. I didn't originally stream, but because overclocking made my system much faster than what it was, I was able to stream all my games. Now I actually have a following who watch me play, and I'm getting close to making money for playing.
I know in my sig rig I have an i7, but the last 3 years I had an athlon ii x3. I unlocked and overclocked it to 3.4ghz quadcore, which let me stream 720p starcraft2. Quite a big improvement, being able to stream 720p on a $300 computer is pretty awesome. Suffice to say, my i7 build can stream an insanely high quality stream and handle sc2 easily at the same time. It's pretty nice.
Now if you play crysis 3 or bf3, the CPU isn't nearly as imporatnt, but it's still a very integral part of the game and minimum fps is always determined by the CPU.
But back to the OP - yea no way you can overclock on a stock computer. What games do you play? It'd really help if you just told us what computer you had, what components you had, and what exact games you play. We can't really help you if you don't tell us what you are even doing or working with.
You can't overclock on a pre-built computer but you can still buy a graphics card, and you can overclock a graphics card on a pre-built computer. Most games are very GPU intensive, so you could still get a huge boost in performance and an overclock of 20-40% that'd be very respectable further increase.
I don't think anyone told you you can overclock your athlon 64 on stock cooling. That's a terrible idea. The chip runs too hot even at stock settings, whoever told you that was a moron.