Charles' Lamb's "Old China" comes from a collection of his writings entitled, Elia and The Last Essays of Elia. To answer your question first, I believe that Lamb, in describing the faces painted on the china, is simply observing that the artist made the men look much like woman with dainty features, and then made the women to look even more feminine if that were possible. In essence, perhaps their clothing distinguishes the two more than their features do.
I love the men with women's faces and the women, if possible with still more womanish expression.
Lamb notes that he has "an almost feminine partiality for old china," thereby introducing the appeal of these items to men and women. Upon visiting a home, he wants to see the china first and then the art gallery. And as he describes the paintings on the china, the sense of proportion of the figures is off in terms of the distance that separates them. The writer is fascinated by the artistry presented, and we sense that the appeal of these pieces transcends gender, and that Lamb is not the only man to be fascinated by these painted figures. However, the lack of realism regarding the space between the figures may also apply to the features of the men and woman. Perhaps this also alludes to how memories are not always accurate either.
The timeless theme found in "Old China" may be in part what accounts for its popularity. For when speaking to his cousin Bridget (actually his sister Mary), she praises not the beauty of "old china," but the delight they experienced when purchasing such items when money was short. She says...
“I wish the good old times would come again,” she said, “when we were not quite so rich. I do not mean, that I want to be poor; but there was a middle state...in which I am sure we were a great deal happier. A purchase is but a purchase, now that you have money enough and to spare. Formerly it used to be a triumph."
Bridget notes that before they ever bought anything that would belie a certain success in life for the one purchasing it, much thought and planning preceded its purchase. For in the days gone by, they would research the piece, its cost, etc. Bridget declares that at that time, that were more exultant. And in achieving it, they felt an enormous sense of accomplishment. When it was with great impatience purchased and "lugged" home, and when they "explored" every detail, nook and cranny, and even repaired the piece that very night rather than waiting until morning, Bridget asks the speaker:
...was there no pleasure in being a poor man?
She continues and will ask this question again. For in living in "poverty," she believes that they appreciated more of what they had because it was not so easily come by.
The speaker explains that they don't have quite as much money as she thinks, but concedes that living as they once did when finances were scarce...
...strengthened, and knit our compact closer. We could never have been what we have been to each other, if we had always had the sufficiency which you now complain of.
However, he also notes that memory can deceive: physically they can no longer walk so far to carry out their schemes; they are not as young as they were. He reminds her that the memories she cherishes do not include the worries, fears and difficulties she did not favor at that time; instead, he turns her attention to the tea cup, asking her to admire the images painted on its surface—also with unrealistic details.