You've stayed onsite before. If EE is the only reason you are seeing for staying onsite, at the increased cost, then no, IMHO, it's probably not worth it for you. If you really enjoy the other aspects of a particular Disney resort, then that's a different discussion.
If you are the kind of family who tends to get to the parks a half hour early or earlier anyway... and you really want to get some of those EE rides in, first thing in the morning, ...then EE has real value. We found the EE value was most significant for getting done with Fantasyland (MK) with small children. The other EE attractions at all the parks usually offer FastPass anyway, when lines get long, so IMHO, their EE offers less tangible value.
Since we really don't like to get up at 6:30 in the morning while on vacation, we're better off sleeping an hour later and getting to the parks just before 9:00. The last couple of times we stayed onsite, we didn't make it to EE - in fact, we avoided the EE parks, except in the evening, for fireworks. So if EE is the main incentive for you to spend more by staying onsite, I wouldn't say it's worth paying extra for (with the exception noted above, family members who love Fantasyland). JMHO.
