The Munsters and Addams Family
The Smurfs and The Snorks
Living Single and Friends
“Bewitched” and “I Dream of Genie”
9021OC
Well, yeah, they would be.
Joan of Arcadia, Wonderfalls
How about 30 Rock and The Mary Tyler Moore Show?
Young doctors have misadventures in their careers and love lives.
Scrubs and Grey’s Anatomy.
Bill Nye the Science Guy and Beakman’s World. (There was at least one other science show that predated both of them, but it was before my time and I forgot what it was called.)
Mr. Wizard?
Kid’s science show is pretty much a venerable, if small, genre in itself.
Mmm… Airwolf…
I still have two VHS tapes full of Airwolf episodes (with, inexplicably, a Knight Rider ep in the middle just to be confusing).
Hm. I may need to do some surgery this weekend and get the VCR working again…
Remove the light-heartedness and it sounds like you’re describing Supernatural .
Silly, though, it’s got in spades. Watchable? Yup. Rather predictable, tho.
Trading Spouses and Wife Swap
Two very different families trade Moms, with disastrous and hilarious results.
Supernanny and Nanny 911
Nanny comes into chaotic home to try and teach parents how to be parents.
And every other reality show, really. I don’t think a single one’s been done that hasn’t been copied by three other networks.
My Favorite Martin, Mork & Mindy, Third Rock From The Sun and even Perfect Strangers
The Twilight Zone, The Outer Limits, and Amazing Stories were all pretty much the same thing, IIRC.
Lost In Space wasn’t really all that different from Gilligan’s Island, and even The Jetsons wasn’t much more than The Flintstones set in the future…
Both of those shows were great - though I preferred The Chronicle and only ended up watching SU2 because as I passed it I thought it was The Chronicle.
The both of them are also in the same general ballpark as Buffy the Vampire Slayer.
Then, of course, their more serious cousins - I’m sure I’ve seen examples other than Kolchak the Night Stalker and Supernatural, but I can’t remember them.
On a related note MiB and GvsE are essentially the same show, save that MiB is aliens and GvsE was demons. (And MiB lacked the great cheesy 70s vibe.) Secret group of agents, who give up their old lives, to protect the world from paranormal threats that they can never know about.
After their plane crashes, the survivors must band together to survive when they are marooned with no hope or rescue
1969 The New People ABC
1999 Peter Benchley’s Amazon, syndicated
2004 Lost ABC
2005 Flight 29 Down Discovery Kids
And there was The Lost FLight. a TV movie with LLoyd Bridges that was a pilot not picked up.
Flip That House! and Property Ladder, currently
They were very different. On Married with Children the daughter was dumb, on Unhappily Ever After, the son was dumb. 
According to Wikipedia, " Both shows were co-created by writer Ron Leavitt, and several writers worked on both shows."
I liked them both, both were very low-brow but in many ways more realistic than the average sitcom crap.
[QUOTE=Martini Enfield…Lost In Space wasn’t really all that different from Gilligan’s Island,…[/QUOTE]
Actually same premise, same star: Gilligan’s Island and Dusty’s Trail.
and wasn’t the science-fiction/fantasy western The Adventures of Briscoe County Jr. uncannily simular to The Wild Wild West?
No. these shows weren’t the same at all. On Friends there were 3 men and 3 women, and one man and one woman were brother and sister. On Living Single there were 4 women and 2 men, and 2 of the women were cousins. See, completely different. 
No, I don’t watch too much TV, why do you ask?