With regard the rarity of the vase, I've managed to find the information I'd found originally on the Cloud Glass site
‘Normally one surface of the completed piece was treated to give it a matt appearance. The majority of examples found today are like this. It is rare to find cloud glass which is polished or matt on all surfaces. Such pieces are sought after for their rarity.’
This is in combination with it having the block that is also matt. I don't believe the block is a marriage, as it would be too difficult to find a) one that fitted and b) one that was matt as well. So I think it originally came with the vase as a two piece.
ooh I've just thought, I've got some black plinths somewhere upstairs. It might look great on one of those. (it doesn't, the black drains the turquoise)
I'm no further forward in finding a matching 'drawn up ' block rather than a domed block. I had thought that maybe the mushroom posy vases might require a block like this as it occurred to me their sides are straight and narrow so getting a domed block out of one of them might be difficult? but I've not managed to find one yet.
The silver epergne centre has to have been deliberately put in as it is riveted in on the bottom, although whether it was made specifically for the vase, or adapted from a previous item I don't know. But it does seem the dates match in era.
I've attached two more pics that are slightly better lighting, but this is a nightmare to photograph. The matt surface does not allow the deep turquoise colour to show well at all