Every Xojo developer should have it in his tool chain and enjoy the features. It has many features and depending on your needs, you may decide which feature is worth the price. For myself i mostly use it to automatically convert my example projects to HTML files to include them in the documentation. In other cases Arbed helped to recover corrupted project files and to compare two versions of a project which have been modified independently without version tracking software. It is also useful to bundle a project with all required files if you need to send a project to a client.
Arbed is highly automatable and can be scripted. You can call it from command line in your shell scripts to do various actions in batch operations. If you need, you can use it to obfuscate strings (e.g. SQL queries) in your application or prepare it for localization. Anything automated which saves a few hours is worth the money.
Arbed is available on tempel.org for $29 or $89 USD.