Caveat: I'm not familiar with Wallet.
After reading this article, my guess is the reason why users prefer 1Password is because of its browser integration and ability to auto-fill web login forms and the like depending on browser URL. This is one of 1Password's key selling feature.
Evidently Wallet does have some form of auto-fill, but it only supports Safari. 1Password supports nearly every major Mac browser. Also, according to that article, you have to type in your password every time you visit a new site and need to login. It may be more secure this way, but I'm sure most people prefer to automatically login if they have unlocked their keychain (which of course can be locked after a set period of inactivity.)
If I'm reading Wallet's homepage correctly, for device-to-device synchronization, a premium subscription is required. The data is then synched to Moxier's servers. 1Password uses the popular Dropbox (referral link) service for its synchronization, and is therefore free. (A basic Dropbox account includes 2 GB of free space.)
So, for those two reasons alone (easy web logins on every browser, free device-to-device synchronization) I would not replace 1Password with Wallet. If you don't require these features, keep on truckin'.