If I had to tally a vote on this based on your situation I would vote "No".
I have two exactly opposite opinions on this matter. I see merits in both options and this argument above to not get the park hoppers is as good as any.
While obviously, having the option to go back and forth is great, it's not absolutely necessary. Yes, the two parks are close together, but sometimes midday, the process of exiting one park and entering another can be a little lengthy, especially if you go from DCA to DL.
Basically, whatever you decide will be fine.