a more dense illusion?

[Silk]

What is meant by a denser illusion?

Denser as in "heavier" or "more filled" with Light. The Light becomes greater :idea:

Can things be more real, more clear?

Yes. Only Infinity is Real. Creation is the Grand Illusion

I associate growth with freeing myself of illusion, but illusion becomes denser?

As long as One is within Illusion, One can only be "free" to explore/experience the Limitations of its own Creation. True Freedom rests in Infinity (beyond Creation). It is the Freedom of Infinity which creates this apparent Limitation. Yet both states may coexist ever-presently, neither one negating the other (a paradox to be sure)

...is spiritual gravity more like gravitas suggesting a weightier sense of value or meaning?

Spiritual gravity refers to the forward/upward/inward "pull" of the illusion-bound entity towards Infinity. Conceive of Infinity as the center ("Black Hole") of this gravity. As One gets closer and closer to Reality, this spiritual gravity increases. Hence, it's naturally slightly greater in 4D than 3D. Spiritual gravity gains more meaning in 7D