David Wolf writes a defence of Mozart's Sinfonia Concertante.

This was never one of my favorite pieces until recently.  I found it
well-made, but nothing special.  However, recently, I heard the Louisiana
Philharmonic (a third-tier orchestra) led by JoAnn Falletta with Elissa
Lee Koljonen and Roberto Diaz as soloists.  The ensemble between the two
soloists amazed me, and the orchestra stepped up to the occasion.  This
was great music-making in any venue (if only the rest of the program had
lived up to it).  So I had a very good chance indeed of cracking the piece.
On the other hand, I'd heard fantastic performances of that work before,
including the Primrose-Heifetz David mentions and the Szell, and had failed
to make a dent.  This time, however, it actually came across as profound
(particularly the second movement), due mainly to the soloists.  I now hear
the work in a different way.  *This* is the reason I go to live
performances:  lightning may strike.

Diaz is, by the way, principal violist with the Philadelphia Orchestra.
A beautiful, rich tone.  Koljonen (a beauty, by the way) apparently has
a solo career.  I can't vouch for her in something like the Brahms or
the Tchaikovsky, but in the Mozart her playing was lyrical and sweet -
"touching," I guess.  Diaz and Koljonen are husband and wife.

Steve Schwartz