Regular readers know that our solution to most dessert/baking problems is whipped cream, and we see no reason to abandon ship now.
Have you tried the cake? Is it horrible? It may not be as bad as you think. Some people have had a bottle of allspice on their shelves since the last millennium, and if that applies to you, it may have lost half its flavor anyway.
If you have tried it and it is horrible, we recommend half the cake and double the plain vanilla ice cream, or sweet cream ice cream, or whipped cream, or crème anglaise – something plain to tone down an overspiced cake. Another option would be to serve a sliver of cake melded (somehow) to a sliver of pound cake, or even sandwiched between two pieces of pound cake, glued with ice cream. Also, a nice chocolate sauce might make you overlook too much allspiciness.
If you are not intending to eat this fruitcake, but share it as a gift, well, any number of clever comments come to mind, but the truth is, you would not want to give it to someone without tasting it.