I got Mel some months ago and I wouldn't say I'm disappointed in him or anything, but he's definitely not a top tier premium character to get. On the plus side, the studio is a nice addition and he's got outside tasks, but on the minus side, his "voicing" is pretty rudimentary, his 24-hour task is him wandering around town with his hair straight, and his best task requires you to buy the cannon, which is also premium.
If I only had enough donuts for one or the other, I would... not get either Mel or the mansion and just wait until Halloween to see what premium items that quest brings.