Outside of your script, are there plans for a user to open this Excel spreadsheet using Excel? If so, you may be close to or exceeding the max number of rows for a worksheet depending on which version of Excel that you're using.
Pulling up the help in my Excel 2010, I found the following information:
"In Excel 2010 and Excel 2007, the worksheet size is 16,384 columns by 1,048,576 rows, but the worksheet size of Excel 97-2003 is only 256 columns by 65,536 rows. Data in cells outside of this column and row limit is lost in Excel 97-2003."
If there's any potential for the number of rows to significantly increase, it sounds like you'll have issues opening the file in Excel. Just wanted to point out this limitation that your exceeding (Excel 97-2003) or getting close to exceeding (Excel 2007, 2010).