My response is that this would depend upon the financial aid policies at the schools that you are applying to. Many colleges only offer financial aid on the basis of need. Your family would need to complete the individual financial aid applications for each school that you apply to. Based upon the economic circumstances of your family and the total cost of tuition at the colleges you apply to, you may be offered financial aid. So, a diverse educational background studying abroad for your senior year would have no influence on the amount of need based financial aid.
Some colleges do offer merit based aid.
This would be in the form of scholarships. In order to be offered merit based financial aid you would need to do well in all of your high school courses. So, whether or not you study in the US or go abroad would not necessarily be as significant as how well you did in the courses that you completed and if you took advantage of the most challenging curriculum that was available to you. You mention that in planning to be away for your senior year that you would take the SAT and decide which colleges you wanted to apply for during your junior year. You will want to keep in mind that you may need to schedule interviews with admissions officers at the colleges you plan to apply to.