I think the OCT is a nice size, because they won't do as many weddings each day as a large resort like the Barcelo will. I also have 65-70 guests travelling, and am going with the Paradise Package because it accomodates 40 guests (then you pay an additional $45 per person for the private dinner reception etc). I think the OCT is also great for a bigger group because if you are like me and looking for a non-beach ceremony location, they have a few other options (Rooftop terrace/Lobby terrace) that accomodate large groups.
You're right - there is no disco at the resort. But the sports bar/restaurant is open all night and that is where the party-goers usually go. It opens up by the pool bar, so not a typical disco - but apparently they have a dj and people dance.
I have heard great things about the service at OCT, which is one of the big reasons we want to go there.
Hope that helps.