Good move for both Flair and WWE, as Flair can now take bookings that either honor him (ala the NWA Hall of Fame deal) or offer up unique photo ops (like the ROH Kobashi one) that he'd missed out on due to WWE. Plus, WWE can still release plenty of classic Flair stuff on 24/7 or DVD, and bring him in for a show to cut a promo every now and then if they so desire.
I almost want Flair to do a promo for TNA just so Mike and Don can have 1,000 collective heart attacks at a real legend SELLING OUT THE IMPACT ZONE!!!!! and say OH WE KNOW WHO THIS IS! when the first few notes of his legendary theme hit. Flair doing something for TNA certainly could work - he'd be great for a Sting send-off (hopefully in a venue more grand than the Impact Zone) given that he made Sting's career in one match 20 years ago. I don't want to see them have one more match together - the bow was wrapped up on their feud when they had the final Nitro match ever - nothing they could do in TNA could top that historically.
As for Joey, he was usually good, sometimes very good, and rarely awful, but was vastly overrated as THE GREATEST COMMENTATOR EVER!!~ by some - he was excellent for a low-budget show like ECW as he spoke in a manner that didn't insult the fans' intelligence, but did have to be post-produced a great deal for ECW's TV shows. He was perfectly fine on live PPV, but I wasn't fond of the usual 20+ minute "Joey yells OH MY GOD and something happens to Gertner to get him off PPV because he's horrible" skit that took up time on a show I paid $20 for (not his fault, but still something that irked me about his act in latter-day ECW).
His MLW run was...fine, although he was clearly just phoning it in (like everyone else in that company), I could've done without him doing a horrid AJPW LAAARRRIAATTTOOOOOO impression whenever Kojima wrestled, he wasn't horrid, and at least attempted to add to what was going on in the ring, which is more than I can say for TNA's broadcast team.
His WWE run wasn't what it should've been, as WWE treated him like a third-string guy, which led to that great worked shoot promo on Raw, but also led to him being stuck in the abyss known as ECW. I don't think he was good enough in WWE to warrant being THE lead announcer for an extended period of time, but I'd at least have more faith with him in that role than someone like oh...Michael Cole, since he still loves wrestling and has a genuine passion for it that can't be faked on-air.