Depending on the types of video you play, your sensitivity to dropped frames, and the overall power of your CPU (whether it is a Core i3 with a HD4000 versus a Core i7 3770k makes a big difference on its own), you can see improved performance with ROHQ mode selected and the hardware acceleration enabled. Possibly a dramatic improvement, or perhaps almost none, depending on those factors.
It will not improve the quality of the video you see (in as far as the quality of the individual frame renders), but it can improve the smoothness of the playback, if ROHQ pushes your CPU too much on its own.
Even with this all in mind, the performance improvement will generally only show an impact when you playing content that requires either:
1. Big up/down scales (upscaling a SD video to 1080p, or 1080p to SD)
2. Complex deinterlacing (deinterlacing 1080i content, for example)
And only in ROHQ, and even then, if desired, you can easily tweak ROHQ to reduce the quality of some of the filters (and you may or may not notice the difference), and you should have no trouble with any modern Ivy Bridge CPU.
So...
Probably not, in your case, if you say you're seeing no trouble.
However, if you DO see trouble when you enable ROHQ with certain "difficult" video files, then a modest video card can go a long way. The developer of LAV codes primarily with Nvidia hardware, so that will probably be the best supported (as opposed to AMD). There are some discussions of specific models for this purpose on
the Video Card board on Interact.