From the perspective of sea level rise, the 0.8m by 2100 is mostly in the latter half of the century, not the earlier half. If you are only worried about up until 2050, I would no be concerned. I would also keep an eye on progress of sea change, and erosion of the beach locally over the intervening years with a view to getting out when it may start to affect value.
When will it affect the value? That is a really difficult question because it is all about perception.
Personally, I am greatly concerned about seal level rise, and global warming. I have a farm in an area that will become more arid and has already been a recent recipient of a cyclone, when the local regulations do not expect it to be a cyclone area. I will ensure any future additions or repairs to the house and sheds are cyclone rated, so I cover my self. I am also aware that water scarcity will be an issue. But I am not prepared to sell it as I want it as a winter residence when we retire.
I guess what I am trying to say is if you plan to keep the place forever, then it is a concern. If you plan to keep it only for 20 - 30 years, then I wouldn't worry.