Speaker technology doesn't change that much whereas AV Receivers are updated annually. They don't change that much and large updates are introduced every 3 or 4 years when the 'next big' thing arrives. At present most, if not all AV Receivers can handle HD Audio (DTS HD Master Audio, Dolby True HD) via HDMI, passthrough 3D (HDMI v1.4) etc. This year's models tend to be adding things like networking, airplay, 4K upscaling.
I would definitely recommend you visit a dealer and arrange a demo of some new equipment. Obviously how big a difference new equipment and new speakers will make will depend on how deep your pockets are and how good your hearing is!