Mark N wrote:

The beauty of building your own boat is that you can equip it best for how YOU will use it.

True.
The problem is that a lot of us are much better woodworkers than paddlers.
I 'didn't have a clue' when I built my first canoe - didn't know how to paddle at all, really.
And it was the same when I built my first sea kayak - a S&G guillemot from Nick's free plans.
That boat didn't have decent deck lines OR decent interior fittings/padding, so rescues or even bracing would have been extremely difficult.
Once I started getting some instruction and learning how to paddle, some 'direct advice' (!!) from experts got me to pay attention to making my boats functional, not just pretty.
And, you cannot trust 'big name' kayak companies to 'do the right thing' with boat design and rigging.
My regular paddle group had a 'rescue practice day' a couple of weeks ago - most of our regular day paddle routes were forecast to be very windy. More than one commercial kayak had sections of deck with no lines, or just as bad, with elastic cord instead of deck lines. It's no joke grabbing an elastic 'line' in the middle of a rescue when you expect a firm connection to a boat. And, a kayak without perimeter deck lines is almost impossible to rescue, or even tow.
The boats we build may well end up being paddled by somebody else in situations different than the ones we put ourselves in on our regular paddles. We have a responsibility to those folks as well as to ourselves to make our boats as safe as they can be. A couple of days ago I was paddling with my regular group which included a visiting paddler in a borrowed boat. The conditions deteriorated (20 knots ) and the visitor accepted a tow to get around a troublesome section on the return. The borrowed boat had excellent 1/4" deck lines end-to-end, so it was no problem clipping in the tow, even in bouncy conditions.
I'm willing to be bet that most expert paddlers (and I don't include myself in that group) would think that a kayak with good deck lines and end toggles was more beautiful than one without them.
I can't understand the thinking behind leaving deck lines off a kayak.