I like all your points, but option 2 is very intriguing. I've never had the time for that, given I use all my mental and physical capacities for my day job. So I'm conflicted; I just don't think I'd have enough time to do a side project to the standards I'd expect of myself.
I think that's also why many posters here are saying 'use some new language feature X to make your work project more exciting' - basically adding a side project into your day job. [I think that road can lead to ruin, if you're making it harder on the next person to work on the code. Be careful and considerate.]
I'd agree that design and building are separate tasks and they can easily become too complex for one person, so it's best if it's divided. As long as someone 'owns' the design (for good and bad), it's less frustrating as a builder.
It sounds like in OPs case, vague specs means not good ownership of the design.
I think that's also why many posters here are saying 'use some new language feature X to make your work project more exciting' - basically adding a side project into your day job. [I think that road can lead to ruin, if you're making it harder on the next person to work on the code. Be careful and considerate.]