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...)
