Seriously, I think of DCA and DL as one big park. We have passes so park hopping is just so easy. As others said, you can hop back and forth to eat, drink, get Fast Passes, etc.
On a busy day when it's jam packed with people. And maybe a random elephant stampede. Sure, it could take two whole minutes.
We are about to go to our first WDW vacation and did not buy hoppers for that but we ALWAYS hop at DL. When one park closes a lot of people hop but a lot also look at the tired little ones and decide to call it a day.
We recently spent 5 days without the hoppers. We still got everything done we wanted to do and most of the time we didn't like we were missing out on anything. If we had hopped we probably would have felt more overwhelmed with a bigger space available at a given time. Instead, we just focused on each park one at a time. But if it's in your budget, it would be really nice to have that option, especially if you are going for an even number of days (DL takes more time than DCA). And it would be nice to just book dining reservations wherever or plan the shows on whatever day you want about worrying about which park you are in on which day. So go ahead and get the hoppers if you would like, but if not, don't worry, you will still have an awesome time!
Personally, for my family, DCA is still not a park that we could spend a whole day at. I mean if we HAD to, for some reason,I guess we could fill the time. We usually hop once a day for sure, sometimes a couple of times.
One time our friends were going for their son's b-day and my son really wanted to go. We didn't have APs then so we bought a one day ticket to DL. We spent the whole day there no problem.
Like everything else, it's all a matter of personal preference. Like a PP said, if going for more than 2 days, get the PH. Have Fun!!