It will make more in April/May than it will make in the winter but probably not a huge amount more than the cost of the service and MoT. If you have to re-tax, you get the balance of that back from the DVLA when you sell. I think you'll have an easier time selling it in the spring when there are more buyers. Right now your most likely customers will be dealers trying to beat you down and buy cheaply in preparation for Spring.