Contrary to common opinion, home test kits for reading soil pH do provide pretty accurate results - far more so than other home soil testing kits....IF you follow the directions properly and use distilled water :-) Given your zone designation, I'm assuming you are in California, which does tend to towards alkaline soil conditions in many areas and also an alkaline water supply.....a double whammy! JaG's advice is valid, however should be tempered with the admonishment that altering the soil pH substantially or permanently may be difficult and heavily influenced as well by soil type. The effects are temporary and will need to be repeated periodically. It may be easier to garden in raised beds with imported soil that has more suitable characteristics. Agricultural sulfur is fully approved (certified by NOP) as an organic application for a variety uses including that of a fungicide, a miticide and as a soil amendment. It is also a very necessary plant nutrient that is sometimes deficient in many soils.

Well, what you have there is a link to a Powerpoint presentation by Doug O'Brien at Cabrillo College. Sadly, all it proves is that Doug O'Brien of Cabrillo College doesn't know what he is talking about if he thinks you get a downward pH adjustment of 0.1 every time you put a ton of lime on an acre of soil. Neither calcium nor sulfate has a direct effect on soil pH and that's all that gypsum is...calcium and sulfate. The only time you will have a downward shift in the pH due to gypsum application is when it is applied to a sodic soil (i.e. SAR greater than 15) which has an elevated pH due to that sodium imbalance. (On a side note, very often the text book rise in pH does not accompany sodic soil conditions) Only when sodicity causes an elevation of the pH does gypsum help decrease that pH. And even in those cases the effect is indirect and has to do with improved soil structure allowing for the leaching of sodium rather than any reactions that calcium goes into. If you need to lower your soil pH, elemental sulfur is your better bet. As far as why it is important...it is primarily a nutrient availability issue. If the pH is too high or too low, fewer nutrients will be available for a number of reasons. Also, if it gets really low you can start having toxicity issues. I guess if you want to get into it more we can start a new thread.

Yes, I do find spot composing can sort of help one plant at a time. You want the soil to have water go right in it. Even if you only dig down a five inches and put compost there, it helps because otherwise the water could just sits or worse yet runs off before it reaches the roots. The compost acts like a big sponge and sucks up all the water and makes the water stay right where it should be which is near the plant roots. If it seems too much work, just go it in one small area and you will like the result I hope enough to continue one small area at a time. Like maybe do one small part per month and with in a few years it will all be done, but of then you have keep topping off the compost, but the first time is the hardest. The ground is the hardest to dig in the beginning and it needs the most compost the first time. If the ground is very hard, apply the compost and water then wait a day and then it will be easier to dig. Also its best to make your own compost in bin but you can also buy compost. Peat is not that great, it helps a bit, someone was mentioning peat. It would be great if you could find some company to bring you a truck load of organic compost with no sand, silt, clay, since you got a lot of that already. I found a company that called it vegetable growing mix. Peat is too expensive anyway, when you need a lot, I like bagged wood, mixed with free starbucks coffee grounds which you can get for free. That mixture can be used as a matrix to add your own kitchen scraps or you can dig it right in now. The coffee has lots of nitrogen so there is no problem with the wood causing nitrogen tie up. If you want to do some moderate feeding, I say good ahead. I use less then they say to use, because less is more and they want to use a lot and buy more from them. I use maybe half of what they say in feeding.

There really isn't any shortcut to this. You need to repot everything with fresh potting soil. You do not necessarily need to move each plant into a larger container but you DO need to replace the soil. Potting soil degrades, compacts and loses its ability to drain quickly over time. The fact that you think you need to add soil to the top of the containers is clear evidence of this. As is the state of the plants growing in it - they are suffering. While I wouldn't ordinarily recommend it, even the cheapo potting mixes available at places like Walmart or Home Depot are better than what you have now. At least for this growing season. Consider it an investment in your plants :-)