Well, one issue can be insurance. You should really declare the car as an import as it is not a full Uk spec car. When the Irish Ed40 were on the market, most of them appraered to be fully loaded cars, maybe this is why they struggled to sell in a relatively small market? The insurance issue down to spec can be a different alarm system, that is not the same as UK cars. I am sure I have seen a few Rhd Ed40 without the lower grill camera sensor which means it is unlikely to have the city crash facility. This was a great help in keeping insurance down on UK cars. (A fully specced car will probably have this, and ACC but it may not be down as standard equipment). On that basis, insurance may be higher on an import?
When these cars are older the value will be determined by condition, history, and possibily rarity, whether we will be allowed to drive one is another matter.
Personally I wouldn't pay up for an Irish import now, they were sold cheaper on the nearly new secondhand market than equivalent UK registered cars and would still expect them to be a slightly harder sell today.