1) I tend to update it as things change in diablo, though I haven't seen any changes lately that require any changing. I still have plans to add some things, like another damage reduction column.
2) You are welcome to use any or all of it in whatever way you want. Otherwise, yes, substituting your dex values for the int column willgive you the right dps numbers, but only if you aren't dual wielding. The spreadsheet so far does not support that, mostly because I haven't played any of the dual wielding classes enough to actually like them as much as my wiz. Also, that will give you the wrong EHP, since Int does give AR, but you can fix that by putting your int value in some AR slot and dividing by 10. There might be some issues with base stats for the different classes at 70, but otherwise it can work reasonably well for a wide variety of comparisons.
The calculation of the gain from INT is off due to an error in cell H25 of Equipped Calculations (drastically overvalued). It's incorrectly still including the Enchantress buff as +0.03 APS while cell H16 also includes it as +3% IAS. Removing '+0.03*'Equipped Items'!$U$23' from the formula in H25 resolves the problem.
I made some updates to the spreadsheet for the latest patch and added a first attempt at firebird dot calculation. It's mostly meant for a rough comparison between gear sets as the actual value should be higher in game due to legendary gems and strongarm bracers. Please let me know if there are any errors.