Hi Emily,
I am happy to hEAR you and your husband are planning a trip to Walt Disney World Resort next year! I have made many adult trips myself, for conferences, runDisney events, and for girlfriend getaways and I enjoy them every bit as much as the trips I take with my kids.
If you are looking to get a sense of the best times of year to travel for lower room rates (and reduced attendance in the Theme Parks), just think about the school calendar. In general, during the times of year when schools are in session you will tend to find lower rates. If you can, try to avoid traveling during significant holidays (Easter, Thanksgiving, Christmas) and during the summer months when families are enjoying their summer vacations.
Some of my favorite times of year to travel is early May and during the months of September and October. This is also generally when you may be able to benefit from reduced room rates and special promotions. While this is not a Disney owned or endorsed website, for more specific information about historical discounts and promotions offered at Disney World Resort hotels, you may wish to consult MouseSavers.com. They have information on past room discounts and promotions going back to 2013.
Emily, if I could chose any time of year to enjoy an adult trip to Walt Disney World Resort it would be in September or October coinciding with the
Epcot International Food & Wine Festival. During this time you will also get to see the beautiful fall and Halloween decorations at Magic Kingdom Park, and perhaps even have a chance to attend a
Mickey's Not-So-Scary Halloween Party.
Good luck with the planning and please let us know if you have any other questions!
Trish