Hey Brian,
I thought I'd look at this just a little differently.
I started with 365 separate files using your ' RunningTally' file's data for contents (assuming right or wrong that this was your starting point).
I changed the field delimiter to a semicolon, so it would not collide with the date-string (using BBEdit's Multi-File-Search).
The first script takes ~ 1 second to read and write all the files as textual data. (The serial dates are just for demonstration.)
The second script is a simple example of reading using delimiter [delimiter] and until [delimiter]. It strips the last semicolon and the linefeed off the end of the record.
With open for access it's easy to read a file line-by-line until EOF to process the data.
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set mailManagerFldr to ((path to desktop as text) & "Mail Manager Folder:")
set dailyTallyFldr to alias ((path to desktop as text) & "Mail Manager Folder:Daily_Tallies:")
tell application "Finder"
set tallyFiles to files of dailyTallyFldr as alias list
end tell
set _date to current date
set time of _date to 0
set collaterFile to mailManagerFldr & "2012_Collation.txt"
set fRef to open for access collaterFile with write permission
repeat with i in tallyFiles
set _temp to read i
write ((date string of _date) & ";" & _temp & linefeed) to fRef starting at (get eof of fRef) + 1
set _date to _date + (1 * days)
end repeat
write linefeed to fRef starting at (get eof of fRef)
close access fRef
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set _file to alias ((path to desktop as text) & "Mail Manager Folder:2012_Collation.txt")
set _record to items 1 thru -2 of (read _file using delimiter ";" until linefeed)
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