Sounds like you will have to find a way to share the iPad with your spouse. Actually, you and your wife can both have all of your email accounts on the iPad, in the native Mail App, or one of you can use the browser version (if one is available).
Another way to keep things "separate" is by organizing all of your apps and folders accordingly. For example, all of
your apps/folders can go on screens 2 and 3, and all of
her apps/folders can go on screens 4 and 5, and then keep all of your neutral apps (Safari, Maps, Weather, YouTube, etc) on screen 1. -- You can also create "his and her" photo albums and music playlists to further separate your stuff from hers.
I know it's not same as setting up multiple users, but it seems you're going to have to get creative with it and learn to coexist inside of iOS until you guys buy a second iPad.
Hope this helps a little bit.