Without an exact high-tech "parts list" of my own, and only reading other's posts and sites, I would say that a major defining characteristic of high-tech is the number of components the hobbyist uses to enjoy their hobby. It's quite high…compared to low-tech as I see it.
My low tech-equipment list includes:
50G Tank, Stand, Eheim 2213 filter, 200W heater, 1 96W AHSupply CF light in DIY canopy, gravel, soil, Seachem Equilibrium & baking soda at water changes with the aim of keeping my tank at about 6 KH/GH (my local water is about 2-3 for each).
8 major components.
If it were high-tech it would likely double the WPG, add compressed CO2, regulator/solenoid/PH meter assy (not necessarily all), and I would be dosing "ferts" and "traces" a few times a week, along with weekly water changes. Maybe using water that's been treated with RO/DI and re-mineralized before use.
Most low-tech tank keepers, from my reading, are usually not using enriched gravels either.
This is where El Natural, or "Walstad tanks" come into the picture which seem to be an offshoot of low tech with 3 pre-requisites. The hobbyist will [1.] Include a layer of soil of some sort as an enriched base for their substrate. [2.] Situate the tank where it will receive sunlight. [3.] Use little or no biological filtration leaving the plants to consume the products of the ammonia/nitrate cycle. (my plants struggled and algae thrived while I had biological media in my filter, now I have only foam and about 1" of fine media).
I suppose some would contest that I am not keeping an El Natural tank since it gets no sunlight after September and only a small amount during the summer months and I use some chemicals to alter my water conditions. I even recently resorted to using H2O2 to slow/stop the algae that had continuously developed while my filter had the bio media in it. The plants are now thriving, I am sucesfully growing (in 1 tank) l.repens, h.difforms and h.polysperma, b.monnieri and b.caroliniana, s.subulata, a.nana, m.pteropus and c.wendtii. c.balansae. I recently added a.reineckii and c.crispulata balansae which seem to be doing well, but it's only been about 2 weeks. Some grow better than others, and there have been a few flops, but I think that was my inexperience and choosing plants that wanted a lot of light.
I am however, trying to adhere to the methods and tactics in The Ecology of the Planted Aquarium since I admire the notion that the El Natural method seems to be striving to build a glass encased pond rather than a "plant tank". The fish and snails and all the little critters we can and can't see are key components, contributing "fertilizer" by way of waste, ammonia, CO2. A big plus: less frequent water changes. There also seems to be a much longer life span between tear downs of El Natural tanks.
I'd say that's my 2 cents, but this turned into a 25 cent post!