If you like the speaker why change? A quick google search tells me this is quite a highly though of vintage speaker.
http://www.vintage-speaker-review.com/2012/05/pioneer-hpm-150-hpm-1500-speaker-review.html
It certainly wouldn't hurt to compare them to some more modern speakers if you have the chance but don't think you need to change them just because they are old.
http://www.vintage-speaker-review.com/2012/05/pioneer-hpm-150-hpm-1500-speaker-review.html
It certainly wouldn't hurt to compare them to some more modern speakers if you have the chance but don't think you need to change them just because they are old.