We drive to Disney and always arrive around 10:30 on a Sunday morning. We find it well worth the extra $25 to go from a 6-day to a 7-day ticket. We usually drop our stuff in the room and unpack a little, have lunch at the resort, and then head to EP for the afternoon/evening. On our last trip (first one with
Genie+/ILL), we had 4 rides stacked before we even got to the park at around 2:00. We did 6 or 7 rides, had dinner, and we were back at the hotel by about 8:45 so we could finish unpacking and get a good nights sleep before doing rope drop at DHS the next morning. And the bonus was that since we got a bunch of rides in at EP on arrival day, we could sleep in on our 2nd EP day and get to the park around 10:00. I think it's well worth spending a few hours at a park on arrival day if you're going to arrive in the morning or very early afternoon. I'd keep it a casual pace and just enjoy hitting up a few rides and maybe a nice dinner.
We used to just hang out at the resort or go to DS on a arrival day because we didn't want to pay for another day on our tickets. We booked the Buy 4/Get 3 free deal (for hotel & tickets) back in 2009 which meant we had that extra day of admission and really enjoyed spending a few hours at EP on arrival day. Then I noticed that it would only cost us about $20 to add an extra day to our tickets on future trips and we've done that on every trip since 2009. It's a nice way to ease into vacation.