It's a simple wire!
The point of soldering is for mechanical benefit, not to reduce resistance. Anyone is more than welcome to fuss not with it.
This will likely open a different can of worms, but I did ask FBO if they had solid coil wires for sale. The response was:
FBO said
Absolutely NO you can't run a solid core wire you'll get constant RI (radio interference) causing constant miss fires.
I've run solid (including the coil lead wire) for over 40 years with no such problems. Yes, with neither resistor plugs or caps. I'm special? Maybe FBO's HRR688 has a problem with RFI? In fact, I've had one of their boxes sitting IN a box for years, was planning on putting it in...which is why I'm looking for a new coil lead wire.
The fact that RFI exists and makes noise in (probably AM) radio does NOT directly correlate to, '...therefore you can't use one in an ignition system.' Now, if it is known that an HRR688 can't run with solid wires, I would think that would be in the literature for the product. I don't recall ever reading such a thing. Besides, there was NO mention of that box in the FBO response I received.
Maybe it's one of those, 'Don't go swimming for an hour after you eat,' ideas, or, 'Salt in your diet increases the risk of heart attack,' or, 'If your cholesterol # is over 200, you need to be on medication for the rest of your life!' Maybe it (the RFI idea) is a facTOID that has worked its way into the 'Things We Know to be True' database that has
no basis on which to be there in the first place.
Some spearminting is on the way, I'm sure.