I think there is merit in your argument; having something more tangible than an idea means a lot more, especially when the op sounds like he is quite open with his ideas and willing to express that initial excitement.

Maybe restraining yourself from this might make you work towards having something more substantial that you can then in turn "show off".

Ok, I agree with this now, but it's different to what you originally stated; "Don't tell people what you are working on until you finish it."

I'd say "Don't tell people what you are working on until you start it."