As for the supposed "parallels" between Oxford's letters and Shakespeare's work, the examples I have seen have been singularly unimpressive; Shakespeare's works are so vast and cover such a wide range of situations that you can find Shakespearean parallels in virtually anything written in English, especially anything written between 1570 and 1630. As an experiment, I picked a letter at random from the Calendar of the Manuscripts of the Most Honorable, the Marquess of Salisbury, a collection that includes most of Oxford's letters. The letter I picked was written by Edmund Williamson in prison on March 19, 1595, and addressed to William Waad. This letter is 279 words long, and in those 279 words I found no fewer than 15 parallels in Shakespeare's works, some of them quite close. If I repeated the same experiment with another letter, or with all the letters of a given writer, I don't doubt that I would find a similar rate of parallels.
E of O's mention of "the most mundane discussion of business matters" brings me to the content of Oxford's letters, which is not quite what Oxfordians would have you believe. In typical Oxfordian fashion, E finds the single letter addressed to Shakespeare deficient, because: (a) it does not refer to him as a writer, and (b) it is primarily a request for a loan, such financial activity presumably being incompatible with poetic genius. Well, first of all, I don't see any reason why Quiney should have mentioned Shakespeare's being a writer in a letter of this kind (there are virtually no such mentions for other contemporary poets/playwrights either), but even if he had, does E of O really expect me to believe that the Oxfordians would pack up their bags and go home? If they can rationalize away the First Folio, the monument, the Parnassus Plays, Ben Jonson's testimony, and all the other evidence, one letter would be no problem: they'd just say it was a forgery, or that it was really addressed to Oxford, or something.
But what gets me is the standard Oxfordian show of horror at the content of this letter, and at William Shakespeare's financial dealings in general, when in fact Oxford's letters do not paint any more flattering a picture (at least from an Oxfordian perspective). Most of Oxford's letters which have survived are from the 1590s and early 1600s, the very period when Shakespeare's plays were starting to be performed and published. All these dozens of letters give no indication that Oxford was writing plays or poetry; rather, they give the impression of a very bored, aging nobleman, fretting about getting back into the Queen's favor and constantly pestering Lord Burghley, and after his death his son Robert Cecil, for something to do. Could he please be appointed President of Wales (see, for example, Oxford's letter of February 2, 1601); could he be made Governor of the Isle of Jersey (July 1600); could he please have the stewardship of the Forest of Essex (May 18, 1595)? Much of Oxford's correspondence involves proposed moneymaking schemes; in 1594-95 he appears from his correspondence to have become obsessed with the idea of farming the Queen's tin monopolies. Of the forty Oxford letters that survive, fully 18, mostly to Burghley, are devoted to explaining in detail how he could improve the Queen's revenues from tin if given the chance (see Oxford's tin-mining letters). Let me quote from one of them, dated March 23, 1595:
"Where it is said the tinners shall have their money lent them at 8 L. in the 100 L., whereas they have it at 10 L.; this is but a mask, for they already have it at 5 L. and 6 L. the 100. And the whole sum so commonly lent them from divers engrossers is not, among them all, above 3000 L. To leave the country to an uncertain price as heretofore, is to return to the former discontentment, before at their own asking it was yielded to them that they should have (communibus annis) 24 L. the 1,000 lb. weight."For the rest of the decade Oxford continued to harp on tin, until he seems to have given up this scheme around 1599 in favor of renewed pleas for the Presidency of Wales (March 1601) and the keepership of Waltham Forest (May 6, 1603). (It is perhaps worth noting that the word "tin" does not appear once in Shakespeare's works.)
Now, if you don't like Quiney's letter to Shakespeare, I don't see how you can like this collection of letters. William Shakespeare became a wealthy man through the theater, and he not surprisingly invested his money in order to provide for his heirs; it is no great shock that the one letter to him which happens to have survived for 400 years should be concerned with business matters, given that most of the records which have survived for people of his social class tend to be legal and financial records. But for Oxford we have dozens of letters from the last 10-15 years of his life, and they are all concerned with various moneymaking schemes and pleas to be appointed to public office; in several of them Oxford explicitly states that most of his time over the last year(s) has been spent in pursuing the latest of these schemes. B. M. Ward (in his crypto-Oxfordian biography of the Earl) and Charlton Ogburn (in The Mysterious William Shakespeare) gloss over these years and make it sound as if a shroud of mystery descended on the Earl, but Oxford's own testimony in his letters show him quite busy worrying about tin tariff rates and suchlike, and not about plays. Charlton Ogburn's explanation for this is that Oxford's enemies went through all his letters after his death, destroying all those that mentioned his play writing activities and leaving only those that presented him in a bad light; readers are free to judge the plausibility of this scenario for themselves. Note that I am not saying that any of this proves anything, but I will say that Oxford's letters have to count as evidence against the Oxfordian thesis, and that Oxfordian handling of this evidence has tended to be disingenuous at best.