Better late then never ;-)
The reason the excel importer sometimes returns floats is because excel only stores numbers as a float. Internally excel only uses text and floats in the program itself it uses a display mask to show a float as an integer or as a date. so if you import an integer or date from excel directly to a string it will show an float.
Solution for importing integers to string, there is a microflow provided with the module: FormatInteger, if you select this microflow in the property: format with microlow the float will be rendered as integer.
Solution for importing dates to string, usually this should work. However it is really easy to make this go wrong. For each cell it is possible to set the content type, (number, other, default or date). If you select the correct type here (date when you are showing a date) it should import and format the date the correct way.
unfortunately excel is really nasty in storing the dates and providing information about the possible ways of storing those dates, so it is really hard to support all cases. If you find a case where the date could not be imported please email it to me and I might be able to support that case in the next release of the excel importer.
(completely offtopic) woohoo! You've posted the one thousandth question! Congrats :)
As to your actual question, I'd either create a virtual attribute that converts it to a string or write a microflow that converts it post import.