I upgrade constructors to restore double constructors. This is a hugely more powerful tactic than you would think at first. What it means is, once you've built a few constructors, you don't need to build anymore constructors as you can keep refreshing your existing constructors. This frees up a huge amount of production at your shipyards, due to the fact you no longer need to constructor spam. If you are playing peacefully, you can then start demolishing your factories on your planets and build research labs instead. You can then build a "bureau of labor" and set the planet to 45% research, 45% income and 10% manufacturing (to avoid coercion penalty), and set "research project" as your production project. This will give you a ridiculous amount of research and enough money to upgrade your constructors indefinitely. Don't get me started on how powerful it is once you can build triple constructors.....
To use this tactic, you will probably need a second constructor design called something like "double constructor reload" to allow upgrading of the constructor to the same design (you cannot upgrade a constructor to the same design template even if you have spent one of its construction modules).
I think a good fix for this is to make ships return to shipyards for upgrades. Or, failing that, prevent upgrading to any ship design that has a construction module.
My personal favorite though, would be to allow the AI to use this tactic too, because upgrading constructors takes much less micromanagement time than managing constructor production at shipyards and star bases.