>> I even raised it another foot last summer because I wanted better drainage. The garden is now 2 1/2 feet above ground level. Moisture is my main concern, particularly excess moisture in late winter/early spring.
I think that most people think "raised beds" to get root zones above peak water tables.
I went the other way and have lowered my "high-water mark" by trenching below my slightly raised beds. Even a few extra inches might make a difference in raised beds with 8-12" walls. Since you have 30" of root zone towering above grade, surely those beds don't need any more drainage! I would have expected the walls to let so much water escape that you couldn't keep them moist.
I eventually amend and re-use most of the clay that I dig out of trenches, so I guess "I go both ways".
You would need at least a little slope to your yard for a trench to carry away water.
I found that a wide trench with a perforated hose was not necessary. Even a small, open slit trench was enough - literally 2" or 3" wide.
I wonder whether some powered edging tool might dig a wide enough trench to let water in the soil under your raised beds escape more rapidly? If not, it would probably loosen the soil in a slit that you could then widen easily with a mattock blade or small-bladed hoe or cultivator. Digging out a slit trench with a spade held "sideways" is rather clumsy, and most hoes would dig a wider trench than is necessary to carry off a little ground water.
