... I'm pretty comfortable with ADODB...

Then you might be glad to here, there is DBD::ADO .

1) all sheets are assumed to have the same columns

You will find it hard to write a generic importer. at least you will have to declare the structure of the excel files, which fields to import etc. Import data into MS-Access is a textfile to access importer, that might give you some ideas.

(2) all Excel data is rendered as of "text" (varchar) data type in Access

Spreadsheet::ParseExcel's cell object supports a "Type" property that returns the kind of that cell ('Text', 'Numeric', 'Date'), so you could use this for your datatypes.