Hi, just came over from your DHS TSM question post and real quick scanned your PTR....our trip dates are overlapping, and we are surprising DD(6 almost 7) with our trip as well. (She doesn't have a clue, she is a total WDW addict and talks about it all the time, but only knows we are going in October.)
So....on your question above, while it's extremely rare to have Spectro after Wishes, it does occasionally happen. (Usually on busy days there are 2 Spectros, one before and one after...but on this date (4/21) it appears only to be after.)
I personally would skip the Wishes dessert party. I have heard many bad reviews for the quality of the desserts, and I can vouch that the location is not the greatest for Wishes (though it's pretty good). So NOT worth the money. The BEST is to stand just south of the hub. If you want to leave right after Wishes, you can still get through the crowds pretty quickly if it is just you and DD. When leaving, a lot of people will be sticking around for Spectro...head into the stores on the right side as you head down main street. (Not, Casey's, but the one just past it.) They are all connected together inside, and you will be able to get through the crowds much faster. (Make sure to check the calendar when you get there...they may throw an 8 PM Spectro in there at the last minute.)
A bit of other advice...the #1 thing that new travelers to WDW do wrong is to not know what they are getting into and not make a plan....the #2 thing they do wrong is plan to do too much. I worry with your schedule you are falling into the second category. Your DD is a bit older than ours, but ours couldn't handle the pace you have. (And she is a WDW-vet, this being her 5th trip). Late nights and early mornings take their tolls after a few days. I am not telling you to change your plans, I am just suggesting that you go into it with an attitude of being flexible, and understanding that you may need to cut some things out of your plan and not be too disappointed.
Quite honestly, as veterans of many trips now - I still find that 10 days is not enough to see everything we want to see - and we don't squeeze in Discovery Cove. If you get yourself too exhausted you simply won't be having any fun. Just remind yourself that you will come back again.
And to answer your other question - yup, I think the crowds will be pretty good sized - a lot of Northerners (NY and Mass both at least) have spring break that week too...another reason we are making it a short trip and dragging it into the following week...hopefully avoiding the worst of the crowds...it won't quite be easter crowds as the Southerners are all back in school, but I expect moderate crowds that week.