One of my favourite phrases is "there is no such thing as a free lunch". Any kind of tweaking has a price, whether it's extra heat, extra power drawn, shorter component life, or an increased risk of BSOD. In my view you have to understand up front whether whatever gain you might make is worth the price. In addition, the law of diminishing returns comes into play eventually and the gain those last delicate tweaks (are claimed to) offer are often so small as to be not worth the effort.
IMO it's better to have a PC that meets 95% of your performance needs and which last 10 years than to have a PC that you've tweaked to meet 98% of your performance needs and which lasts only 5 years.
