A few comments:
The most potent pot I've ever had was seeded. It was "William's wonder" from 15 years ago, and I'd put it up against anything I've had before or since.
The biggest difference between seeded and unseeded is in WEIGHT. Seeds take up a huge percentage of the weight of buds, so since virtually everyone is buying and selling by weight, seeded stuff doesn't go nearly as far. On a per-plant basis, you'll get less yield of bud from seeded plants, it will take more work to de-seed for smoking, and the stuff will take up more room. So you don't want to be growing seeds for personal use or for sale. But if you take seeded weed, remove all the seeds carefully without disturbing the trichromes, and compare the bud that's left to similar unseeded weed, the seeded will still be nearly as potent as the unseeded.
In fact, I believe that famous breeder DJ short has speculated that seeded plants may actually be BETTER because their cannabinoid profiles are different, partially explaining why the stuff from the "good old days" was better. Nice theory. . .though I don't know if its true or not.
On THC content, this idea that today's plants blow away everything from 20+ years ago in terms of potency is one of those pernicious urban legends, mostly promulgated by those who want to convince you that pot is more dangerous than it was 30 years ago, or those who want to sell you seeds. Its FALSE. You can't trust the gov't numbers, and yeah, you also can't trust the numbers published by the seed-sellers. Even the honest ones are only publishing their numbers from the best samples taken at peak from the best parts of their best plants.
Here's a now ten year old article touching on some of these points:
http://www.slate.com/articles/news_and_politics/hey_wait_a_minute/2002/11/the_myth_of_potent_pot.html
Note that I don't think sensimilla was particularly rare 10 years ago, but the general points still hold true.
Cannabis has been selectively bred by humans for roughly 10,000 years, as long as ANY plant has been bred. During that time, of course people were breeding for maximum potency, and its probably fair to assume that the plants maximum potential potency. . .or pretty darn close. . . has been reached in many different places over the years with many different strains. Hash more potent than ANY marijuana has been readily available for literally centuries.
THC is simply NOT higher in today's plants. . or more precisely, the best plants from 30 years ago are still up there with the best stuff around right now. The big differences are that THC is measured differently today, yielding totally different numbers, and that strong weed is more generally available now..
30 years ago, it was grind up entire sample (which was unmanicured buds including low-THC seeds and fan leaves), throw into machine, and come up with percent THC as a portion of weight.
Today, its take only the best tops of the totally dried, trimmed and manicured buds, and measure the THC as a fraction of trichrome weight (not even total weight). So of course the numbers are going to be much higher when you measure this way.
My understanding is that if you take the older "classic" strains, and measure them using the same modern techniques, they hold up percentage-wise to today's "super" strains.
Next issue, is that Reagan's "war on drugs" greatly reduced the influx of cheap outdoor grown pot smuggled over the borders. With more and more people growing indoors in limited quantity and space, there has been more emphasis on improving potency. In other words, the stuff today is more potent, not because of any major genetic breakthroughs, but because nobody bothers to grow the less potent stuff any more!
I think today people only care about the qualities of the main big buds, so naturally that's where the highest concentrations of THC are found in the plant.
