I could not find an option in the recent version of Google Spreadsheets to change the text line height (the spacing between lines in a single cell). You realize the problem even more when exporting the spreadsheet as PDF, the lines are very close to each other which makes it uncomfortable to read.Summed up, it would be helpful to adjust line heights. I like to give the text lines some spacing to each other (one long line, no splitting of the text over different cells). 
How to change the text line height in one cell?
google spreadsheets