In regards to job fairs to obtain an interview at Spirit Airlines I would say if you can attend one then do so, it will definitely help.

If you have a strong internal reference that is willing to write you an internal letter of recommendation you will probably get an interview without attending a job fair in our current hiring environment.

If you do not have an internal reference and you are not getting a call within a month of your initial application date then I would start looking at attending a job fair.