Snipped...
This past few months I did 2 dives in Ft. Lauderdale and 2 dives in San Diego. Each time I felt jacked up on my first dive. I was frustrated with myself that I didn't have better buoyancy or better breathing rates. Then I realized, everything's different, the circumstances are different, so dive #1 = find the adjustments you need to make. It's not as much fun to be down on that first dive knowing something is off and it needs to change, but that's what dive #1 is all about. Between dive #1 and dive #2 in San Diego I dropped 8 pounds of weight! Man, it was nice to get that extra weight off and Dive #2 was much much better! And that's how it always is, Dive #2 is much better!
Like you, I dive when and where I get a chance. I've done surf entries, boat entries, cold, warm, salt, fresh, drifts for both salt and fresh and they're all a little bit different the first time out (so far anyway). The only places I've dived more than once are my local quarry and BHB in West Palm Beach, FL. Add to that gear tweaks and nothing is ever exactly the same.
I am religious about keeping track of conditions, including my weight, exposure protection (down to gloves and booties thickness), surface and depth temps, equipment I used/carried, where I carried it, and of course a fair amount of verbiage about how I felt during the dive on top of the details I like to keep about what I saw. I'm slowly dialing in a calibration matrix that gives me a good basis for what to start with on a given dive.
I will say, though, that 8 pounds seems to be too much adjustment. I've never had to change more than 4 pounds and that was adding weight to accommodate the addition of a second wetsuit for a night dive when I got unexpectedly cold during an afternoon dive in Hawaii. (I don't use a lot of weight though so that could be part of it...)