We are WDW vets and if it was WDW, I would tell you that park hoppers are not that big a deal- we usually get them there, but we don't use them every day, although it is nice to have some flexibility and we do use them here and there (especially our last trip when we were trying to get as much done before a hurricane as we could). However, I would go nuts without park hoppers at DL/CA. We usually are in the parks around 4 to 4 1/2 days and we hop every day at DL/CA, sometimes several times a day. To us, being WDW vets, it is like one big park. It literally takes 5 minutes to get out of one park and into the other and you do not have to go through bag check between parks (the parks are connected by a plaza and you go through bag check on the outskirts to get into the plaza). We have been from the back corner of DL to the back corner of CA in 10 minutes. It is an entirely different experience than hopping at WDW. We hop if the lines at one park are getting long and the app shows them shorter at the other. We hop if DD suddenly wants to go get in another ride on RSR with us all using the single rider line. DH has been known to hop for the sole purpose of going to the Karl Strauss beer truck on the pier at California adventure- he will disappear from DL for 20 or 30 minutes (usually while DD and I ride Small World for the 2nd or 3rd time) and then reappear. Literally, we can get in a 10 or 15 minute line for Small World, ride the ride, and then walk to Main Street and meet him inside DL after he has already been to CA, had a beer and walked back. Often DL stays open later than CA, and we almost always hop over when CA closes to get more DL time. I think they usually open at the same time now, but a few years back, CA used to open a little later most days, so we would go to DL for the first hour, and then hop to CA when it opened. We stay at DLH and last summer with the new security we wound up in line for 30 minutes our first day to try to get through the metal detectors. The rest of our trip, we just went to the parks about 10 or 15 minutes after they opened, used the GCH CA park entry and then if we wanted to start at DL, we just immediately hopped out of CA to DL. Even in mid July, just waiting a couple of minutes past the morning rush, we never waited more than 5 minutes at the GCH gate. So- at least for us- hoppers are important and a big deal at DL/CA and it would drive me crazy not to have them, while I could easily forego them at WDW and probably not feel it too much.
NOW--- all that said--- if the only way I could get 2 more days in the parks was to forego hoppers--- I think I would take the 2 extra days hands down. It would drive me crazy to be restricted to one park or the other- but 2 more days at Disney seems like a no-brainer. So, I do think from that aspect if you can not do both you made the right decision. Now, if you can do both, you may still want to consider it. Even though you have bought the single day- you can always add hoppers if you get there and decide you would actually use them.