The cheapest upgrade is changing the rubber surrounds of the mids. They stiffen / harden up as the years go by. If they are (a lot) stiffer than those of the woofers then changing the surrounds will improve things a lot.

I’ve done this upgrade on my old 5500's, the 7200's and 2 weeks ago on the SE upgraded 7200's. The difference is quite big. And the costs about 10 pound for the pair...

Before mounting the mids back in their enclosure, I had them play 24 hours with a sweep between 5 and 20 Hz to play in the new surrounds.

Some Meridian...