In fact your receiver is very likely of higher quality than a lot of the systems today. Just make sure any new speakers you purchase will work well with thew amount of power your amp delivers. Obviously relatively efficient speakers (rated 88 dB or above) will work better with the less powerful amps of the past.

For home theater, a lots has changed (even from 10 years ago). Modern uncompressed codecs keep increasing the dynamic range of soundtracks driving up power requirements. Digital cabling keeps changing, etc. But good speakers are still good speakers regardless of the age.