Candy Dulfer did a cheerful version of Miles Davis’s “So What?”
Sheryl Crow pepped up GnR’s “Sweet Child of Mine.”
I’m at a loss to find the “original” version of “Iko Iko.” Some sources call it a Traditional, some trace it back only to the 1950s. But the three covers of it I’ve heard. by Dr. John, Belle Stars and Zap Mama, all get progressively more upbeat, and those are not happy lyrics.
“Man of Constant Sorrow” belongs on here somewhere.
First: There were the morose undertones of Siouxsie and the Banshees original 1980 version oh Happy House
Some 20+ years later, Ginger Ale’s happier & peppier Electronic Cover pushed the upbeat envelope.
Blind Melon had a very cheery cover of the Velvet Underground’s “Candy Says.” If you wanted to, you could actually dance to the Blind Melon version.
There are also a couple of Richard Cheese covers that turn bleak/sad/stupid songs into something you want to swing to: “Down with the Sickness,” “Creep,” or “Loser” (by some stupid screaming band, Radiohead, and Beck, respectively).
Lama Pacos, the point I’m making is that it’s IMPOSSIBLE for the Sixpence cover to be faithful to the original.
Sixpence’s is a poppy love song of devotion.
The original is an absolutely wrenching look into the longing and dedication that goes with unshakeable addiction.
Sixpence have no way whatsoever to connect to that, no way to express that, and so their version, while musically almost congruent, has none of the merit of the original.
Although they are almost identical, The La’s version is NOT upbeat, while Sixpence’s IS, simply by nature of who they are, and they ruined the song because of it. It’s not the music notes that make the song upbeat or depressing, it’s the meaning.
Happier, more upbeat cover of Cyndi Lauper’s “True Colours” was done by Phil Collins.
Try the Greatful Dead version.
Er, Grateful Dead.
In the movie “As Good As It Gets,” Jack Nicholson is constantly playing a cover of “Always Look on the Bright Side of Life” in an upbeat, played-straight manner.
You’d never guess that it was originally an ironic song sungby cricified people in Monty Python’s “Life of Brian”.
Th recent cast recording of “Spamalot” has a very upbeat version of this song as its closing number (and they use it in the commercial).
Rufus Wainwright covered “Hallelujah” for the Shrek 2 soundtrack and tried to make it an upbeat song.
Which, if you’ve watched the West Wing, is impossible.
Jeff Buckley’s tortured, haunting cover of the song plays behind Secret Service agent Simon Donovan being shot during an armed robbery and C.J. Cregg’s subsequent tearful walk around downtown Manhattan.
Krokodil, if the Dead is still to upbeat, try Mary Knysh or Joanne Griffith.
I had to hear Lyle Lovett’s version to really get the meaning behind the words.
You’re quite likely right… Though apparently Bananarama also did a cover, as it is listed on their Greatest Hits compilation, so I’m not 100% sure which 80s-girl-band cover version I am hearing in my head. Double brrr!!!
Rudy Vallee’s cover of “Brother, Can you Spare a Dime?” made it all peppy and bouncy.
I’ve been listening to Susanna Hoffs and Matthew Sweet’s Under the Covers Vol 1. She tends to be the lead on most songs and the following are a bit peppier for it:
Cinnamon Girl
The Kids Are Alright (!)
I don’t think they are being ironical.
Johnny Cash covered Nine Inch Nails, the name of the song escapes me but while it was still a depressing song. I can at least listen to his cover around my mom without her thinking I’m a satan worshipper 
It’s been a while, but that version didn’t strike me as particularly upbeat. Wasn’t that during the longing-montage scene when Shrek and Fiona were separated?
Fun Boy Three released “Our Lips Are Sealed.” The Go-Go’s released the same song shortly after. Two very different versions of the same song, written by Terry Hall (FBT) and Jane Wiedlin (GG).
Barenaked Ladies’ cover of Bruce Cockburn’s “Lovers in a Dangerous Time” is a tad peppier than the original.
The only NIN song Cash covered AFAIK is Hurt. But ‘happy’ and ‘upbeat’ aren’t exactly how I’d describe it.