No, just dressing well and being nice won’t get you an upgrade.
Airlines save valuable business/first class upgrades for their elite frequent flyers — if they give you an upgrade just for dressing well and being nice, those who “earned” it would be pretty upset.
That said, if you experience extenuating circumstances such as a severe trip disruption, a broken seat, or other major inconveniences, you could definitely ask to be upgraded.
The worst they can say is no…but if you’re dressed well, ask nicely, and there are seats available, you may have your request granted.