Whether the tax returns are legally required is totally irrelevant. Romney cannot be compelled to release his tax returns, but his failure to honor modern ethical standards would be a negative during the campaign.

Only a tiny percentage of tax returns are audited. Seeing the manner in which Romney is evading taxes, it is a legitimate question as to whether he is not releasing older returns to prevent illegal actions from being revealed. It is also a legitimate question as to whether he has managed to legally pay even a far lower rate than he admits to.

Monitoring of conflicts of interest after elected can be too late. Many voters will want information on this before the election.

It would help him for his campaign or his supporters to remind people of that.     

You are correct in that there is nothing illegal about the net rate paid by Romney on his taxes.  He’s in a position where he can take full advantage of the US tax code (capital gains being taxed at a lower rate than income, have funds/investments off-shore, etc).  And assuming the IRS has been doing their job, his historical tax returns would have already passed audit checks and/or are currently under review.   (Looking online, I don’t see anything saying where he is currently being audited.)  Now, should he better explain why he does have funds/investments off-shore?  Sure.  It would probably be politically beneficial to those who are uncertain about him, though I doubt it would satisfy those who are already against him.  That will be something his campaign will have to address.  Of course, the obvious question is, knowing in 2008 that he would probably run again in 2012, why didn’t he close those accounts four years ago to avoid any impression of impropriety?
 
Lastly, as far as your comment about conflicts of interest, you do have a point (not addressed in my quick note in my article).  Any candidate – from the Romney’s and Kerry’s down to the Obama’s and Dole’s – are going to be exposed to a certain conflict of interest upon entering office if they have investments.  When elected, the President is required under the Ethics in Government Act to disclose their financial holdings (which becomes a part of the public record).  This way, financial conflicts of interest are identified.  Also, the Act also authorizes independent counsel to investigate politicians, so if a President has off-shore accounts, they can be examined.
 
Thanks for the opportunity to discuss this topic.  Hope this clarifies any confusion from the quoted section above (it about exhausts my knowledge on the topic).  Keep up the good work!
 

Rest in Peace, Sarah Jane