I know my past experience might not be precisely relevant today, but I used to have a decent upgrade percentage even as silver on both DL and US. If I thought I would fly 22,000 miles for the year and one 3K round trip would get me possible upgrades the whole next year, it would seem very much worth it.
In 2009 I was silver on US and the day before Christmas flew LAX-PHL with my then-girlfriend (now wife). Somehow even with me silver and her having no status, we both got upgraded. I know people don't think much of domestic F, but it turned a 5-hour ordeal into a rather romantic trip. What price can you put on that?