If the speakers are Mercury MK1's then they look like this...
I had a pair from new back in '84. They're a fair bit bigger than MX1 which are really a very compact bookshelf speaker by comparison. The Mercury MK1's are standmounters and need a bit of space to the rear and sides to work as intended.
There's no directly comparable product in the recent Mercury range. The old MK1's have the sort of bass depth that would be expected from current floor standers. The top end is sweet but slightly rolled off because of the soft dome tweeters.
These come up for sale every now and then on Ebay. Prices fluctuate a bit. £15-£60 depending which way the wind is blowing. The later MKII's are available for £30-£100.
What to do with the ones you have.... Only refurb them if you intend to keep them. Unless you find a decent s/h bass driver cheap you'll spend more fixing them than they'll return at auction.
The other alternative is to break them for spares. That's what I'd do. You'll have two decent tweeters, one bass unit, a couple of cross-overs (though they'll rarely be required) and a couple of grilles.
The Denon amp is well engineered, and has some nice features - a turntable input and pre-amp outs to drive an extra power amp...it's just that..well, it sounds a bit flat and uninteresting compared to the British amps and the better Japanese of the day. The Rotel RA820bx, Creek CAS4040, or NAD 3020 would have been first choice alternatives for musicality. Creeks fetch £40-£60 on average.
What to do with the amp is a more puzzling question. It's not a desirable "Hi-Fi Classic", but equally it's not tatt either. In fact it'll probably keep going for another 10-20 years if kept clean. Advertise it in the right way - emphasise the phono stage - and you might be in with a shout of shifting it to a vinyl enthusiast/home DJ. The other choice is to keep it and use it with some speakers you've bought with the money from breaking the Tannoys.