Difficult question.
They probably are better generally all things being equal, but the difference might not be as much as you're being told.
My Tannoy Berkeley's were built in 1978 and I'd say they still outperform 90% of speakers built today. But they were a fairly high end design back in the 1970s.
On the other I had a pair of Heybrook HB1s back in the late 1980s and I doubt whether the £170 cost back then would amount to more than £500 today.
What I don't doubt is that the HB1s would hold their own against anything this side of £500 today.
Of course both those speakers were pretty special for their time and no doubt there was a lot of crud back then too.
So perhaps it's fairer to say, mainly because of advances in measurements and testing, that there's just a lot less rubbish out there today?
If I was you, I wouldn't bother with any supposedly incremental upgrade.
When the time comes you might want to look at something that promises a serious undeniable improvement. Depending upon what you have already it could be something from B&Ws own speaker lineup or a different brand.
@jnovak
The next time you're at a hi fi show walk past a pair of $100.000.00 speakers and have yourself a little chuckle.
Quite true.
But preferably not in front of its designer if you can help it.