As provided in this Act, the issuance of College Savings Bonds is in all respects for the benefit of the People of the State of Illinois, the conduct and increase of their commerce, the protection and enhancement of their welfare, the development of continued prosperity and the improvement of their health and living conditions and the issuance of such Bonds is for public purposes. In consideration thereof, College Savings Bonds issued under the General Obligation Bond Act in accordance with this Act and the income derived therefrom shall be free from all taxation by the State or its political subdivisions, except for estate, transfer and inheritance taxes. For purposes of Section 250 of the Illinois Income Tax Act, the exemption of the income from College Savings Bonds issued in accordance with this Act shall terminate after all of the bonds have been paid. The amount of such income that shall be added and then subtracted on the Illinois income tax return of a taxpayer, pursuant to Section 203 of the Illinois Income Tax Act, from federal adjusted gross income or federal taxable income in computing Illinois base income shall be the interest net of any bond premium amortization.