I think you're underestimating the beakers. "Only a rep scientist" is pretty decent when it doesn't use any citizens. It adds up to over 1100 beakers in 100 turns (with academy, library, and a monastery), which of course means you are getting useful techs faster along the way, so it's really even more. Couple that with the quite significant production boost to build useful buildings/troops/wealth, and I think you are really missing out if you leave a GE lying around for too long.
Other things to consider are an AI beating you to what you were saving it for anyway, and the fact that it locks you to a particular path, when it might be necessary to change suddenly in response to DoW or something.
I've used a GE for oxford too when it was going to take to long otherwise, so as per usual it's situational for me. I probably am too quick to settle though.
Edit: Also, whether or not the capital is hammer starved is somewhat irrelevant. Adding a free mine to any city in the early/mid game is very useful!
Other things to consider are an AI beating you to what you were saving it for anyway, and the fact that it locks you to a particular path, when it might be necessary to change suddenly in response to DoW or something.
I've used a GE for oxford too when it was going to take to long otherwise, so as per usual it's situational for me. I probably am too quick to settle though.
Edit: Also, whether or not the capital is hammer starved is somewhat irrelevant. Adding a free mine to any city in the early/mid game is very useful!