Jeff,
Increment by one and similar operations is most easily achieved using Evans Formula plugin (Which includes date handling) or others that use the maths.js library.
I am lobbying for such increments and item counts to be in the core, soon we will have the range operator that will help in some cases, but dates are another matter
You may increment a week number but of course a week number greater than 52? will most likely be invalid. that is the problem with date handling. Every value needs to be reset and don't tell me about days in the month or leap years/centuries.
If the tiddlers have VALID date fields, with future dates, perhaps populated by the Pickaday plugin, you can use the days operator to find them and once you have that date you can use the view widget to format date to extract the week number.
Regards
Tony