I have this working, using Gnumeric's ssconvert:
ssconvert --merge-to=merged.xls test1.csv test2.csv test3.csv
It happily imports formulae, such as =MIN(G2:G4) correctly.
The problem I have is with off-sheet references.
How do I, with the above setup, get a cross-sheet reference to work?
For example, in test3.csv:
=('test1.csv'.G11+'test1.csv'.G8)
When I try this, if converts the off-sheet references to text. I have tried doing this with LibreOffice Calc and OS X Numbers - I even tried the Numbers reference format:
test1.csv::Table 1::G8
It still doesn't work.