I had a look at Griffiths valuation c.1847-64 for Alexander Spratt to try to help you focus your search.
There were only 3 hits for that name. 1 in Ballynanaghten in the parish of Aghalee Co. Antrim for Alexander Spratt renting land from Abina Spratt. Abina was the lessee from Marquis of Hertford, and was sub-letting to Alexander.
2 hits in Donegal, both in the parish of Conwal. These could possibly refer to one person only as one rental is for a house, office and yard while the other is for land only. The address of the house is 196, Main Street, Letterkenny.
These people are not your Alexander. There are a lot of other Spratts in Ireland but this is where the given name Alexander occurs.
RonnieG