There IS a point of diminishing returns..and dont forget the more tips on the top the less light to the bottom..so the bottom may only get 2g per tip rather than 5. Still thats 2g more than you had before, and with good lst techniques you can minimize or eliminate blocking.
For every day of veg theres a days worth of sugars and starches created and stored in leaves and roots, new leaves and roots are created to store more...its exactly as you say..every day counts...you have to factor in electricity, labour, nutes and drying time for the extra days also...bottom line..just like everything in life theres: Not Enough, Right, and too much.
That being said I am currently undertaking a micro grow. YES I know I could have vegged for longer (hell i could have put it in with the others in the room) But I wanted a tiny tiny budding plant...I joke with her every day telling her i wont smoke her all at once LMAO. So shes topped at her second node then has 2 colas off that. Shes a little Y of buds. Im allowing the 2 "main colas" and the 2 colas from the first node to grow, I will trim any other buds.
Thats novelty though, and besides the point...for a serious no bullshit grow op study your plants growth, when this slows to UNDER a node a day (in your case), you will no longer be gaining more than you are spending.
excuse typos! had a few this morning haha...