Been listening to a recording of a 2009 production of Porgy and Bess, conducted by Nikolaus Harnoncourt. It’s not always as lively as I’d like it to be, and some of the smaller roles are sung a bit too much as though this were Italian grand opera; but all in all the production is very good, very moving, and remarkably clean and crisp, even in Gershwin’s densely written choral numbers. Gershwin’s orchestration is a bit weighty and takes skill to keep from overpowering the singers, and under Harnoncourt’s direction it sounds just about perfect, lush but not heavy.
I’m not wild about the practice, common now, of restoring the cuts that Gershwin made in rehearsals, with one exception. He cut these passages because he saw that the opera flows better without them, and putting them back in just weakens the pacing. The one exception is Porgy’s “Buzzard Song”, which actually strengthens the story and which Gershwin cut only because the original Broadway production was scheduled for eight performances a week and Porgy had three big numbers close together at that point, and this was too much of a strain on the singer’s voice. So one of the three numbers had to be cut for that production, but when the opera is performed on a schedule less tiring for the singers, “Buzzard Song” is well worth including. Gershwin’s other cuts, though, are better left cut as far as I can see. Harnoncourt restores a few of them, but thankfully not the whole lot.
I’m still on my first listen, nearing the end of the second act. Michael Forest’s Sportin’ Life seems like the standout so far, but really, most of the cast is terrific.
Scratchings 
Have you heard the Houston Grand Opera’s 1976 recording of the complete Porgy and Bess. If not, you might want to listen to it and compare it to this and other abridged versions. Gershwin allowed himself to be talked into dropping a lot of great music from the score prior to its New York premiere in 1935.
I have heard it, yes, but I think that it’s a better work with the cuts Gershwin made — with the one exception of the Buzzard Song. For starters, I think that the opening of the opera, a short prelude leading quickly to the curtain rise and “Summertime” and the crap game, is incredibly effective in the theater, one of the most striking and powerful openings to any opera or other musical theater work that I know of; while the longish piano solo that Gershwin originally wrote to set the mood is effective musically, and I’d be happy to hear it in the concert hall as part of a suite of excerpts, but it’s very weak dramatically; it spoils the pacing of the start of opera and lessens the impact of the crap game scene that follows. It might be different if Porgy and Bess were more of a mood piece in which the story wasn’t as important, but it isn’t; the power of the story is crucial to the strength of the opera, and the crap game scene is crucial to the story. Gershwin’s cutting his piano solo in rehearsal in order to make the opening more powerful seems to me to be a brilliant stroke, the act of a confident and masterful composer for the theater.
It’s fascinating to be able to hear the work as it existed at the start of rehearsals, and I’m glad to have the Houston recording and I’m glad to hear an occasional production of the first draft version, but I can’t think of that as the “complete” Porgy and Bess or of other recordings as “abridged”. Call it the “Ur-version”, maybe. I’ve seen and listened to the opera both ways, and the cuts Gershwin made seem very plainly to me to have made the piece more powerful and effective as music drama.
As I said, I think putting back the Buzzard Song is a good thing; I think it contributes to the overall dramatic tension and doesn’t harm the pacing at the point in the story where it occurs. None of the other cuts Gershwin made seems to me to be worth restoring except as an occasional change of pace.
I would agree with you about cutting the piano music (except that it leads to a return of the Introduction and those increasingly wild harmonies). If I were making cuts I would eliminate the Lawyer Frazier scene. But what about the cuts made to the final scene, when Porgy returns from jail? A lot of beautiful music was left out of the first production. Gershwin didn’t want to do it. He had to be talked into it by the director, Rouben Mamoulian.
I’d have to look at the specific things you’re talking about to refresh my memory. My immediate reaction, though, is that the last five minutes or so of an opera or musical is a bad place to insert anything that doesn’t serve the overall structure of the drama, however beautiful.
I’m talking about in the theater, though; recordings are different.
I think the last scene of P&B, when performed unedited, is consistently beautiful, whether on stage or on a recording. For instance, the 1935 production cut the trio section of “Oh, Bess, Oh Where’s My Bess.” I think it must have pained Gershwin greatly to see this go. We are lucky when a recording or a stage production includes it and all of the final portion of the score.