Picked up a nice Miyata 615 today, hoping to get my father into riding bikes again. I'm having thoughts about swapping out the downtube shifters for sti's...i think he might ride it more with the upgrade, but I'm not totally sure about modernizing this bike. I have an ultegra 9sp group, which shifts great and would work perfect with smaller chainrings and a different cassette.

Any strong opinions for/against modernizing this bike?

Nothing wrong with modernizing it but it may not be so straightforward. If you go 9 in the back, you'll need a different rear wheel and you'll have to spread the rear triangle. The existing crank may not work great with brifters either. Best bet is probably to hunt around for 7 speed bar end shifters or go with friction bar ends like these,

Dia Compe Bar End Friction Shifter Set > Components > Drivetrain > Road Shifters | Jenson USA

3 x 7 brifters are another option, https://www.amazon.com/Shimano-Tourn.../dp/B00GQCC9A0

Bar end shifters are friction on the left; the chain rings on the miyata are not optimized for index shifting. That said, it can work.

Ahh yes, bar ends could be great! The front wheel is a bit out of true, and I'll have to go thru the hubs and make sure the bottom bracket is good to go, but this could be the best and quickest way to go by far.