[Spoilers for Heyer's Venetia very likely in the comments. Also Lady of Quality. Read at your own risk.]

There is a trade paperback edition of John Aubrey's Brief Lives, for those of you who might be interested.

Aubrey, John. Aubrey's Brief Lives. Ed. Oliver Lawson Dick. 1949. Foreword Edmund Wilson. 1957. Boston: Nonpareil-David R. Godine, Publisher, 1999. ISBN 1-56792-063-2

If you have suddenly been seized with covetousness or curiosity, you can order it online here.

And one of the entries in it is Venetia Digby, the same "admir'd Venetia" for whom the heroine of Georgette Heyer's Venetia is apparently named. She was, Aubrey tells us, "a most beautifull desireable Creature" (Aubrey 100)--and I had forgotten that Damerel properly attributes that quote when he uses it:

      "I beg your pardon!"
      He raised his head, still choking with laughter, and said, "Oh, no, no! Sweet Mind, then speak yourself ...!"
      She wrinkled her brow, and then directed a look of enquiry at him.
      "What, lurched, O well-read Miss Lanyon?" he said provocatively. "It was written by Ben Jonson, of another Venetia. I turned it up last night, after you had left me."
      "No, is it indeed so?" she exclaimed, surprised and pleased. "I had never heard it before! In fact, I didn't know there had been any poems written to a Venetia. What was she like?"
      "Like yourself, if John Aubrey is to be believed: a beautiful desirable creature!"
(Heyer 87-88)

But there's quite a lot Damerel doesn't tell Venetia about her namesake. For the passage that describes her as "a most beautifull desireable Creature" goes on to recount: "being maturo vivo was left by her father to live with a tenant and servant at Enston Abbey in Oxfordshire: but as private as that palce was, it seemes her Beautie coulde not lye hid. The young Eagles had espied her, and she was sanguine and tractable, and of much Suavity (which to abuse was great pittie)" (Aubrey 100). And lest you be imagining the Disneyfied version, Aubrey further tells us: "The Earle of Dorset aforesayd was her greatest Gallant, who was extremely enamoured of her, and had one, if not more children by her. He setled on her an Annuity of 500 pounds per annum" (Aubrey 100). She ended respectably, though, marrying Sir Kenelm Digby and apparently being faithful to him: "Once a yeare the Earle of Dorset invited her and Sir Kenelme to dinner, where the Earle would behold her with much passion, and only kisse her hand" (Aubrey 101). She died suddenly at the age of 33.

So what is this lady doing as the patron saint of one of Heyer's virtuous heroines? That we are meant to have Venetia Digby in mind I think is clear, both from Damerel's quotations and from the fact that Venetia's younger and much adored brother is named Aubrey. ( spoilers herewith )I think Venetia Digby's presence in Venetia is a intertextual marker of the same thing the book itself is arguing for: tolerance, perspective, the ability to take the long view. ( spoilers again )Heyer arrays a sense of the ridiculous against respectability and propriety, and we are left with no doubts about where her sympathies lie.
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WORKS CITED
Aubrey, John. Aubrey's Brief Lives. Ed. Oliver Lawson Dick. 1949. Foreword Edmund Wilson. 1957. Boston: Nonpareil-David R. Godine, Publisher, 1999.

Heyer, Georgette. Venetia. 1958. New York: Jove Publications, 1981.