Jimistone, you suprise me being a vintage strat afficionado with your understanding. (Unless I am misinterpreting what you are defining as a "ground issue".
All factory stock vintage strats are NOT shielded and the middle pup is NOT wound to give you noise cancelation in the middle positions. And dependent upon year, sometimes middle positions don't even exist due to having a 3 way instead of 5 way switch.
ALL single coils buzz, or hum or whatever you want to call it.listen to any live Hendrix recording and you can hear it.
ALL strats also have a string ground, and when you are touching the strings the hum decreases. This is normal and the nature of the beast.
I suppose in theory, it should all ground out via the cable shield and the grounding in the amp, but in the real world your body is part of the ground. If that wasn't the case, there would not be a string ground.
On Norlin era Les pauls, they omitted the string ground entirely and shielded the guitar by enclosing the components in those metal cans.
However, despite the pickups being "humbuckers" and the shielding, they still hummed. Installing a proper string ground solved that, but as soon as your hand released from anything metal, the hum returned.
I build and repair guitars for a living and have worked on thousands of electrics and built in excess of 500 instruments ( not counting parts-casters) over my 37 some years of doing this.
It is normal for a guitar to make more noise when you remove your hands.
Shielding helps reduce noise, but not 100%.
The ONLY instruments that I've come across that are truly 'noise free' are those that have active pickups.
To bring up the Norlin Les Paul example again.... I've had clients that gigged with their guitar for years and never noticed it.
Until.......they went into the studio.
In the studio EVERYTHING is magnified.
Most guys never complain about the noises their instruments make untill it's studio time.
In today's age with the home studio, and with super clean digital recording, more noises are more apparent than ever before.
Also, and this is just my opinion, I think we live in a more electrical noisy world. There's a lot of juice flowing around and there's a lot of stuff in the air. I don't know the impact of things like cell towers and wifi, but I'm sure it has some effect. And all these damn "smart" appliances and tvs. Our hardlines and airwaves are polluted.
So as to solutions, shield your guitar, maybe upgrade pickups. (Good pups have a higher signal to noise ratio), clean up the juice in your home with a power conditioner, stay off off lines that are shared with motors. (Fans, fridge, a/c units ets).
As to upgrades on your guitar, everything makes a difference. Good pickups, good quality pots, switches, good caps, as well as wire. I've found the good old 50s style wire with the braided shield to be quieter than the modern foil shield wire. A lot of little things all add up. For strats it's a bit too much to try to rewire with the shielded wire, so copper shielding is a viable option.
Also experiment with times when there is less electrical activity going on.
Also, check your cables and your amp.
A shitty cable can make a hell of a lot of noise as well as a faulty or crap amp.
Ps, an old trick for in the studio. Attach a wire from anything metal on your guitar and tape it to you body. That way when you remove your hand from the strings, the string ground is still active.
Hope some of this helps.