I think you would be best off with a 5 day park hopper plus 2 options (either pleasure island or water park) or just a five day park hopper and buy your pleasure island admission separately if you aren't going to go to a water park.
It sounds like you may spend a total of five days in the parks. I don't think that is enought to justify the cost of an A.P., which I think is actually about 400.00--a little more than you thought.
It might be worth it if you were going to use your A.P. to get an A.P. discount on your room at the Pop Century if one is offered for your travel dates. You might want to check mousesavers.com periodically and see if such a discount exists or becomes available and then see how much an A.P. might save you this way, and if it makes the extra cost worth it. It might. I checked it and it looks like there is an A.P. discount through the end of August that will give you about $30 off the cost of your room per night. That's $150 savings. A five day park hopper plus is about $270 through an online ticket broker like ticketmania. You could also get five day park hoppers without the plus options through
AAA for about $235.00. Figure you'll pay about $250 in park costs without the A.P. With the A.P. you'll pay about $400.00 However, you'd save $150 on your room, so either way--I'd say you'd come out the same. What an analysis!
You also mentioned that you were going to a convention. Do you know if there are any convention park tickets offered for your convention? You could look into that. If there are, covention park ticket prices are often very good.
Hope I didn't confuse you more. It would be best for you to tak a look at mousesaver.com and check out some of her suggestions for park tickets. Others might have other suggestions for ticket comparison sites. I know there is another one I am forgetting. Good luck!