i would definitely split the stay, either once or even twice. you could split the stay between a value/mod/deluxe. or do 2 weeks in a value and end up in a deluxe or a home-away-from-home (villa). there are tons of ways to do it. i've split stays, and it feels like a new vacation when you move resorts... BUT i have to say it was hard for me to really relax when i knew i was going to be moving again. my dh didn't feel that way at all (probably because i'm the one who packs and unpacks everything for our family of 4).
have fun deciding... and good for you being able to go for 3 weeks!!