I'm thinking about a Liquidator as well - few more questions if the OP doesn't mind me re-using the topic instead of starting new? TIA.
1. My location has full sunlight. I can imagine paint on plastic peeling off. What kind of paint works best?
I've had good luck with Krylon paint for plastics. I painted the sky light in our RV shower about 5 years ago and it's still in pretty good shape.
2. About removing salt from the bottom... can the salt be scooped out without empting the tank? Or do you wait until the chlorine is used up and then disconnect/remove the tank for cleaning?
I used the LQ for over a year and now my sis has used it for over a year and neither of us have ever seen enough salt buildup to even notice. It gets cleaned once a year and there's not even an eigth of an inch in the bottom. Some bleach has less salt than others and maybe we're just lucky.
3. How long does it take to get a 2" accumulation of salt in the bottom (mentioned in the manual as the clean-up threshold)? I use around 3-4 gallons of 6% bleach per week for a 25,000 gal. vinyl pool.
See #2.
4. What's the deal with the 3/8" upgrade kit - what problem does that solve?
Some people (myself included) had a problem getting enough flow through the unit due to low suction and discharge head pressures and the 3/8" upgrade helps solve that problem. The tubing is larger but more importantly the control valve is easier to adjust and the check valve is a larger but lower cracking pressure model. I also upgraded the control valve to a Hayward needle valve and it makes fine tuning the flow much easier.
5. Should I expect to use more bleach in the Liquidator than I would pour into the pool without it (after painting the tank)?
You should use exactly the same as manually dosing it.
6. When properly maintained & cleaned, will this thing hold up over the long haul (5+ years)? Do the valves require regular replacement? Does the tank eventually rot and fall apart? etc...
The unit I had is now 3 years old and sits right out in the full sun and it's showing no signs of degrading. The float valves have been changed a couple of times, but they have a lifetime warranty and Hasa ships them right out.