You already owned ST for a long while. Go with something new. I had a ST pro for around 3 years. Enjoyed it and played it a lot during that time. It just got to the point where it was time to move on. My biggest issue was the first level modes took so long to complete. Timers would stop when the ball was in the pops and when you cradled the ball. And if you hit the black hole target it adds even more time. If they made it easier to start modes, shortened level one modes, and had more to do between modes the game would be so much better. I'm a decent player and only saw the 2nd wizard mode twice. MET got an update to make the game easier and take away some of the wood chopping. ST needs the same.
I say go for MB. It's not my favorite game but I think it would be awesome to own one. Playfield is gorgeous and it's about as classic as you can get. Guests will love it. If it was your only pin, it might get stale fast. In a larger collection, it would be great to play when you just want to have fun and enjoy good, campy pinball. If you do get sick of it, it should be easy to sell.