Well, used a mixture of things.

Used the Washington Flyer for $10 to West Falls Church.
Paid $3.85 to McPherson as it was peak time.
Following day bought a 1 day travel card for $9 and used that a bit.
After that, just paid as I travelled as trips were only $1.85 as it was the weekend - easy enough to put $3.70 on a card for a return.

Some Metro stops are not in the best location anyway. Found that L'Enfant to the Capitol Building is around 3-4 blocks and that takes you onto the Mall.
If you get the Metro, you've a walk slightly uphill for a few 100m to the east side / Library of Congress and the better photo opportunities are from the west in my opinion.