The !g (and other bangs) makes the switch seamless. If I don't like the result just rerun w/ !g.
I'd love to know what those 70% of your queries look like.
(One interesting observation: when first switching, I found that I liked the DDG results a lot better when I styled them to look like Google results; they felt more "right" somehow.)
Google proper has several value-adds besides the search results. Solving math equations put in the search bar for example. I usually use a dedicated service for things like converting feet to meters instead of typing it into google.