Maybe someone will find this helpful.
I tried to improve my "searching for barnacles" abilities today, so I went solo, found one of the known barnacles (namely: Pleiades Sector IH-V c2-16 C 4 -1,254 -164,182 ) and did some experiments. Some specs first: GPU - AMD Radeon HD 7900 Series, latest set of drivers, Win 10. Resolution: 1920 x 1080. All GPU settings were set for application to take over.
The goal was to find ingame graphical options that make barnacles more visible and to see what range/angle would be optimal for searching.
By default my settings are all set to High/Ultra, with sliders set to maximum and antialiasing SMAA x1.0. Testing method was: Position my ship (Asp Explorer) at the angle I would usually fly while searching (heli mode: about 40 degrees lean towards the ground), barnacles in front of my view. Distance from the ground 4.0 km. Then I began to tweak settings while increasing and decreasing distance to see barnies easily.
I won't get into details of what settings combinations I tried out (it took a while...

, I will just jump to conclusions. With my default settings I could see barnacle main node from about 4.0 km (knowing where to look). Options which have (in my case) impact on that distance were: Terrain Quality, Model Draw Distance, Terrain Work, FX Quality, Reflections Quality. The rest of the options did not seem to affect it in any way. So, My advice is: for getting the best barnacle visibility you need to set above five settings to maximum. Especially FX Quality and Reflections Quality as those seems to be responsilbe for "shininess" of the barnacle - this makes them more spottable. Without them I had to reduce altitude to about 2.5 km . You could also switch Blur off, and set Ambient Occlusion to High (it didnt affect the distance, but made lighting more friendly).
I would say that optimal altitude for fly by search would be about 2.5-3.5 km. I could see ring of barnacle small nodes from there.
Of course this may be different or even false for other GPUs (or different eyes ;P) so, if someone could try to confirm/deny my findings would be great.