I'm also in a chicago suburb, north shore, we adopted an overlay district in the late 80's in the face of an potential onslaught of real estate offices and other offices that apparently were poised to move into a fairly retail focused district.
I'd probably favor the overlay district approach, making such "non-retail" uses subject to a special use permit, rather than outright prohibit them; otherwise i'm assuming you'd end up with two very similar zoning districts, with the main difference between them being the uses permitted. More importantly, a special use process would theoretically allow, as a safety valve, a particular location to be used for non retail if it the case could be made that it wasn't suitable for retail (due to inadequate size of the space, too far off the sidewalk to support retail, etc).
Our retail overlay district covers the majority, but not all, of two of our core commercial zones, and leaves a third entirely alone, with non-retail office space permitted by right.
Some of the applicable language, particularly the standards for special uses, are liste below. That being said, our overlay district has been fairly successful, and to that end we've been pretty stingy about special use permits for non-retail occupancies (banks, etc).
PM me if you have any questions...
*All of the uses marked with an asterisk (*) in the foregoing list are special uses if they are located on the ground floor in the C-2 Overlay District and within one hundred (100) feet of a public street.Standards
Special Use. As a special use, subject to the conditions and requirements set forth in this chapter and in Chapter 17.56, any one of the following:
a. Any use listed in subsection B above designated by an asterisk, located on the ground floor in the C-2 Overlay District; provided that, in addition to the standards set forth in Chapter 17.56 for the granting of special use permits, the applicant demonstrates that the special use will be in compliance with the following additional standards:
i. The proposed special use at the proposed location will encourage, facilitate and enhance the continuity, concentration, and pedestrian nature of the area in a manner similar to that of retail uses of a comparison shopping nature.
ii. Proposed street frontages providing access to or visibility for one or more special uses shall provide for a minimum interruption in the existing and potential continuity and concentration of retail uses of a comparison shopping nature.
iii. The proposed special use at the proposed location will provide for display windows, facades, signage and lighting similar in nature and compatible with that provided by retail uses of a comparison shipping nature.
iv. If a project or building has, proposes or contemplates a mix of retail, office and service-type uses, the retail portions of the project or building shall be located adjacent to the sidewalk. The minimum frontage for each retail use adjacent to the sidewalk shall be twenty (20) feet with a minimum gross floor area of four hundred (400) square feet. In addition, such retail space shall be devoted to active retail merchandising which maintains typical and customary hours of operation.
v. The proposed location and operation of the proposed special use shall not significantly diminish the availability of parking for district clientele wishing to patronize existing retail businesses of a comparison shopping nature;