How much is it worth? For starters be sure to talk to your insurance agent if you activate it.. Generally THEFT insurance goes DOWN when you activate OnStar..
Why you ask? Well.. As a retired police dispatcher I can tell this story:
Got a teletype to be on the lookout for a stolen Cadillac of a specific model. Read it over a few times, talked to my supervisor and sent a message back to the entering agency, The message contained the 800 type number for On-Star.
A few minutes later I got a 2nd teletype asking if we could check an address.... Yup, it was there.
OnStar found it.