I don't want to stretch all rows and columns to make them more readable than they are by default...
As there is currently no way to add either vertical or horizontal padding, you need to use a workaround to be able to add cell padding. Since these are workarounds, I will add the cons to using them below.
For horizontal padding:
Thanks to Pitter Pat (source) for this method. Essentially you need to change the format of the cell and add spaces to the format. This will ensure the content of the cell is not changed, but the way it looks (in terms of padding) is changed.
Go to Format > Number > More formats > Custom number format...
Type in the following and apply:
" $"#,##0.00_ ;" -$"#,##0.00_ ;" $"0.00_ ; @ ;
This should give you five spaces of padding to the left and right of positive and negative numbers, zeros, and text.
- This could likely mess with custom formats you are using, if you are using anything other then positive or negative numbers, zeros, or text
- This does not add true padding to the right side of a cell. In order to achieve "true" padding, the only way I see is to make a new column to the right of the cell you want to pad and try to make it blend in.
For vertical padding:
This is mostly manual.
You need to select all the cells (click the top left box, on top of "1" and on the left of "A", or control/command + A). Select the vertical align and set it to center. Then, change the height of all the rows. NOTE: this will get rid any custom vertical align/height settings you had for any cells or rows).
Ensure that the text wrap setting is set to anything other than "wrap text" (i.e. "clip" or "overflow").
If necessary, manually wrap text in cells and change their heights.
As you can see from these steps, this mainly has to do with playing around with the rows and heights and whatnot. The cons with this is that it isn't a good, "definite" way of adding vertical padding—if your content changes, you will manually need to change the padding again. It also is quite cumbersome if you rows aren't similar to each other.
My Workaround: Add a skinny column to the side you want padding on, and then make the border between the skinny column and the column you are working with white. Then when you print it looks like everything is moved in however much you want. Honestly, cell padding is such a standard feature in spreadsheets. It's pretty ridiculous that Google Sheets doesn't have this function.