Apple's iWorks Numbers spreadsheet is a step forward in spreadsheet designs, as Numbers liberates the spreadsheet from the 1 table per worksheet paradigm. Multiple tables/worksheet eliminates a whole class of formatting and arrangement problems, as you format and arrange the tables how you please.
Macros the code of spreadsheets are not yet in Apple's Numbers. (Maybe I can influence their design. (Nah.)) What I would like to see is an additional presentation format for macros in spreadsheets. You would still have the macros in the spreadsheet cells, but you could also view a listing of all macros named by their cell location. Furthermore, I would like to see cell aliases, so you can refer to A4:C1 as either "A4:C1" or "Interest rate".
For Numbers, this would give 4 levels of code/macro organization:
File -> Sheet -> Table -> Cell
similarly as to how in Perl and many other programming languages we have:
File -> Class/Package -> Method/Sub/Function -> Statement
Before I would undertake such a spreadsheet macros design, I think I would look at the presentation formats of various math/symbol packages like Mathematica, TK Solver, etc. to see what has already evolved (there's no sense in re-inventing the concept of the wheel, although you may have to tweak the detailed design of the wheel for your particular application). After all, what is a spreadsheet with macros but the common computerized form of a system of equations?