Charles Sanford Terry's <Bach: A Biography> (2nd Edition, OUP, 1933) has 76 illustrations and photographs following the index. It includes, No. 69, another Schwartz painting (reproduced in black & white) dated 1785, from almost the same exact perspective, with more details, including the brick floor. Terry also has, No. 67, "a drawing by Joh. Stridbeck in the Old Rathaus," showing the church exterior with steeples, corniced roofs with stain-glass windows, and the main entrance with a main tower flanked by two bell-towers (with clocks), as well as a Terry photograph, No. 68, of the adjacent Nikolaischule.
Two bits of information:
1) In 1724, Bach forced the Town Council, which ordered him to present the annual Passion at St. Nikolas, to pay for a choir platform installed for safety and space needs. Apparently the interior up front was badly in need of repair.
2) The annual Town Council Installation cantata and special services for the Dresden Court, such as the Thanksgiving and Allegiance services in the early 1730s, were all presented at the Nikolas Church as the official government venue for church services, as well as the official church for the Lutheran hierarchy, such as Superintendent Deyling's congregation. This probably explains the curtained boxes for dignitaries, both civil and ecclesiastical, as well as, I would assume, local businessmen and their families.