How much should a U1800 USCF player devote to strategy?

In your opinion.

I don't know.

IMO players should take an eclectic approach. As long as the material is high quality, try to get a little bit of everything. Strategy is just one of many. I'd say get one good book. I like Pachman's Modern Chess Strategy. I also think of Soltis' Pawn Structure Chess as a quality strategy book.

Silman, Seirawan, Euwe, Nimzowitsch are some other authors to consider.

Then, as you spend more time with tactics, endgames, openings, and general analysis, you'll absorb more patterns and ideas that compliment your strategic understanding.

So on one hand you're not done after just one book, but it's also true that you need to learn other areas to really improve your strategy as much as possible i.e. you can't just read 10 strategy books and be done with it.

I think an 1800 should still focus primarily on tactics.  

1800 with good tactics and strategy makes the 2000