Well to be honest it is more outside of games that I have noticed the benefits from the G15 I recently got. The keys are a bit more.... tactile/spongey than my previous logitech, meaning that I can type slightly faster. The LCD display showing cpu/ram usage is nice (saves having to use a windows app) and the volume dial is very slick.
I've not even bothered using the macro buttons as yet, but they are probably very useful for some games like beat'em ups or RPGs.
It also looks very cool!
I used to have a similar opinion to you, in fact I don't think I've ever spent more than about a fiver on a keyboard until last week. But at the end of the day, no matter what you have 'under the hood' in your pc, it is the peripherals that you interface directly with - monitor, keyboard, mouse and headphones. I've spent around £225, £47, £37 and £70 on those respectively for my current setup.