It would really be nice if custom fields added to a service item in the service catalog could be a selection in dispatch'r and observer within the condition. 

Essentially adding another selection box next to ticket field and requester field to be "service item field"? See image below

another possible idea is the initial selection on dispatch'r or observer on which lifecycle to ad this rule to? Maybe add-in "service request" to separate them?

I very badly need this to happen.  Our intention was to create a service catalog item for our employee onboard process.  Everything worked great until I needed to send an email with some of the details to a distribution group - I can't get them access to those details no matter what I do.  I basically have to scrap the entire idea of using the Service Catalog as a result.

Joseph - I think that the user meant that they need to be able to access the fields within a service item type rather than the type of service item. For example, if I have a service with 3 colors, and want to filter based on color selected using a custom color field within that service item, currently I cannot. I can do it for Tickets, but not for Service Items.