Whether or not a K&N filter is going to be responsible for a noticeable increase in performance depends on the size of the filter and the air flow through it. For example, 90-96 C4s use a huge panel filter. Up to about 500hp, a K&N is no advantage over a clean, stock filter.
You look at other GM V8 applications, such as pre-82 Corvettes, older Camaros and Firebirds or some truck engines and you see the stock filters used there are small and K&Ns can be a significant advantage. This is especially true of engines modified for increased performance but still use a stock-sized air filter assembly.
One thing many don't understand about the comparison of paper filters to the K&N (oil-impregnated, cotton-gauze in a wire framework) is the paper filter's air flow capacity is less tolerant of contaminates. This means, as the paper filter traps dirt, it becomes restrictive at a faster rate. This effect is so pronounced that it doesn't take much contamination before a paper filter will have a noticeable restriction, compared to a K&N with the same amount of dirt trapped. Because of this, in a case where a K&N replaces a paper filter having adequate air flow when it's new, the engine may see improved performance during the period of time that paper filter would have been in the second half of its service life.
Lastly, the biggest advantage of a K&N is it can be reused. Once it gets dirty, you just wash it, dry it, reoil it and put it back in. If you are a finatic about clean air filters, you can do that once a month if you want but you'll never spend a dime for a new filter again.
I've used K&N filters for over a decade and have, no doubt, saved a lot of money because of it.