We just purchased a home and it has 6 pairs of standard grey outdoor lights for uplighting the front of the house. It feels like a bit of overkill, and the boss is not a huge fan of the look.
Are there any good full replacement LED alternatives you guys have used? Or should I just buy some PAR38 LEDs and re-caulk the existing fixtures?

Lowes has some led landscape spotlights that would replace the grey fixtures. I've never used them, but they look better than what you have.

Maybe replace with single bulb lights that point straight up?

I definitely recommend replacing with LEDs. I was replacing bulbs monthly with my lights like what shows in your picture because water kept shorting them out. Switched to LEDs in an enclosed container and problem solved. I had to buy some photography gel sheets in a yellow color to make the light look natural instead of hospital white, but that's also fun because we can put different colors in during the holidays.

highly recommend looking into maxlite LED lights

I did something like these in my house I built 4 years ago and have been pleasantly pleased. Not one failure in 4 years.

https://www.amazon.com/dp/B01DIO7IAO/?coliid=I3US0QYRQ2U6B8&colid=37KX8U5ETKCST&psc=0&ref_=lv_ov_lig_dp_it

Ditch the up lighting and stop contributing to light pollution?

Mostly kidding, all of the big landscape lighting companies typically have a line voltage line with "landscape looking" light fixtures.

See Kichler below:
http://www.kichler.com/products/category/landscape-120v-led-accent.aspx