I absolutely do not accept the "slippery slope" argument and feel I have enough information to see this essential feature request rather clearly - and as follows.
Evernote is a NOTE TAKING application whose primary goal (if i'm not mistaken) is to make it FAST & EASY CAPTURE essential ideas and well, ummm NOTES. Further, it's BUSINESS obligations are / should be to give its users AS FEW REASONS AS POSSIBLE to HAVE to use other solutions, or leave their platform environment AS MUCH AS POSSIBLE.
Numbers (best stored in TABLES) actually 100% qualify as NOTES.
Tables of numbers without ANY formulas are relatively USELESS and SIGNIFICANTLY slow down the note taking process WITHOUT BASIC formulas (see point 1 above).
Linking LOCAL Excel documents (not even SAS cloud spreadsheet integration mind you, like Google Sheets or Office 360) causes SIGNIFICANT issues / slow down / limitation and creates OUTSIDE DEPENDENCIES (not to mention creates a slew of other irritants and ongoing complications like user expense buying additional software, file management / migration of local files, ongoing 3rd party compatibility issues / coding updates etc.)
THUS, BASIC FORMULAS (summing, addition, subtraction, multiplication and division) ARE INDEED ESSENTIAL AND ARE LONG OVERDUE. I'm actually surprised this feature only has 255 upvotes as of this moment, but am sure that's far under representing the percentage of users or potential users (who may not be adopting EN because this basic necessary feature is not supported).
Please - get ON this Evernote! More advanced formulas / functions, like table to table communications (which apparently requires table names which do not as of yet exist in the EN database), percentage calculations (desired but again, could live without for 90%+ of my daily needs at least) and more, could easily wait if these basic tools were provided reliable / robust.