Well, it depends a bit on how you view the situation - for example, if you get a $1,500 Trijicon ACOGS for your $800 AR, that is a not an uncommon situation. The $800 AR will outperform the naked eye and the ACOGS is a top of the line tough optic. Plus when/if you upgrade your AR with a match barrel, and the Timiney 3# single stage trigger, and such, you will already have the optic you need for it.
Fundamentally, the quality of glass is the quality of glass. There are innovations around using aspherical glass to increase the eyebox, and other such smaller innovations, but the technology of a telescope has stayed pretty constant for awhile. Some may argue that the same is true for the firearm as well - and I can't really argue that too much - but to me there is more of an application for a cheaper firearm than for a cheap optic.
The one place where I would support using cheap optics is in the case where the application really doesn't warrant more expensive optics. If you have a Ruger Mini - 14 Ranch rifle and are staying 100 yards and in on a coyote size target then less expensive glass can be had which will do that fine. Or if you don't know anything about red dots but want to try one to see if you like them. Or if you've always used high quality fixed power optics and want to try a variable - to see whether you really want to adapt to messing with the optic in the hunting environment then I'm inclined to say that getting something cheap makes sense.
However, ultimately I'm of the opinion that you settle on the best glass you can reasonably afford for a situation.
Thinkingblade