I think it depends on what you need from a boat.
If you liveaboard or even spend large chunks of time, then the living space of a longer boat is good.
However, if you only want a boat as a weekend getaway or for high days and holidays, then small can be beautiful.
A lot of costs on boats are pro-rata to length. Moorings, blacking, drydock, insurance ?, licence, etc
Also, its easier to maintain a shorter boat - quicker to clean, black, paint, etc.
I have a Northern-max narrowboat too, but the benefits of a smaller boat for some aren't wasted on me.