Universal Studios in Florida is NOT the same as Universal in LA, but if you have been to Universal LA, you probably don't need a full day at Universal Studios in Orlando, plus it depends on how long ago you did Universal in LA.
I much prefer IoA over Studios, but I'd still recommend getting 2 park access so you could have a quick go through Studios. Then at least you'll be able to make an informed decision the next trip
I go to IoA every time I visit Orlando, I've probably only worried about going to Studios one out of 3 visits.
Men In Black is a good fun shoot 'em up (sort of like Buzz LightYear, but not as good as Toy Story Mania (the 3D in that is AMAZING!!!!!!), Jimmy Neutron is very good

. Shrek and The Simpsons are at Universal in LA, so you probably wouldn't need to do them again, unless you want to.
Rip Ride Rockit looks really scary, BUT it's actually not that bad.
Up until last month, I'd have said you could easily do both parks in one day outside school holidays etc if you've been to Universal in LA. Adding Harry Potter to it, I'm not sure if one day will be enough to get through all of IoA! Don't miss Spiderman, it's pretty much like Back to the Future/Simpsons, only better.