Lucky streak

In one of his Christmas cards K was given a scratch card, he won £3 so took it along and exchanged it for three more £1 cards, which he then mislaid.
He came across them today so we scratched them off and the winnings are now up to £5, the dilemma is do we cash them in and buy a (little) treat or do we buy another 5 cards and see how long the lucky streak lasts?