Necessary to upgrade?

I am running 1.2.1 and 1.3.2. Is it necessary to upgrade or do it merely provide some bells and whistles?

The latest version of Omeka provides many significant improvements in functionality and security. New and improved plugins and themes are also only being written for Omeka 2 or higher. So, I'd say if it is at all possible, you should upgrade.

Any customizations to themes or plugins you have written yourself won't work in Omeka 2. You should also check that the plugins you are using now have corresponding versions for Omeka 2 on the plugins page.

So it sounds like the biggest motivator is security?

It is a big one, but the additional features, if there is still work being done on the sites, are significant. If there's no work being done on the sites, it is less important.

thank you