You have enough days to cover both parks without hoppers. However I much prefer hoppers as the parks are very close and if you are heading back to the hotel anyways why not go back to a different park? Also it really helps with teens to let them go over to DCA and ride the coasters /TOT, etc... It is also nice for evening events where you can get FP for F! and spend all day in DCA and come back at night for F! also WOC if it is open.
No they are not necessary... I find we enjoy the parks so much more if we just stay put...When we don't hop, we get immersed in the magic and get to really explore. To each his own and I know I am in the minority.
We are getting 5 non hopper day tickets and staying onsite. I figured we would do three days at one and two at the other. I have read not to cut expenses on this but I plan to do morning and evenings at the park and taking a break in the afternoon. I think we would save $150.
For us, parkhoppers are a must, but I can totally see the argument for the opposite. We like having the option of going where we want, when we want. Especially when DL gets really crowded, its nice to escape to DCA. If you are taking a break mid day, PH might not be as much of a necessity though. Either way, have fun!
We went back to our hotel each day in the afternoon. A lot of times we'd come back after our break and head to a different park. It was quite nice.