If you have other i386 machines around, it may be convenient for you to keep the same architecture so you can share the download bandwidth of Debian updates, and things like that.
On the other hand, now might be a good time to begin the migration to the future. 32-bits will be around for a long time, but it will increasingly be relegated to older hardware and niche applications, such as embedded processors or cell phones and the like. 64-bits is going to be the "current" architecture for desktops, servers, and the like for a good while to come.
MAA