Selfishly, I think you should trade or sell me the last 20 cards I need for my high-grade '77 set!
Realistically, it's tough to say for sure what you should do. There aren't a lot of "no brainier" stars to submit for grading in this set. The base Nolan Ryan, probably. Maybe the George Brett? Even the HOF rookies (Bruce Sutter and the multi-player Andre Dawson) are amongst the least desirable of the '70s. If you have a really good eye for picking out 9s and 10s there's value in submitting the right stars and tough commons, I'm sure. Then there's the questions of cost, time, which grading company, etc.
There will certainly be trade (and purchase) demand if you want to move them individually, but to maximize your value/return that way you'll be spending a lot of time and effort... and inevitably will still have a pile of them left that couldn't find a home.
Depending on your collecting goals, you could always sell them as a lot and turn a little profit, or keep them in your collection, either as a start to a really nice vintage set or just as an increasingly rare stack of 40+ year old mint cards.
Good luck with whatever you decide to do!