Well, speaking from experience, I've owned 7 MM to date, 1 of which was new-out-of-box with about 10 plays. This was all pre-2003ish. Honestly I bought these to re-sell. And they did. I figured when the prices on these stabilized that I would just save a nice one as a keeper in my collection and leave it at that. The last 2 or 4 that I had picked up were so banged out and nasty that I became not too hopeful at finding a halfway nice one. At this time HEP's were going for around 9k so at that point I figured these had out priced 'keeper' status.
Then the beaters crept up to 7+ range which in my mind was insane. The prices for this pin always amazed me but it is what people want. Then they announced the repro's and I figured I'd let others test the water. Most of the feedback is pretty positive except for all of the most pedantic of Pinsiders <rolls eyes>. Anyway, I picked one up a few months back and am really impressed with it. Bottom line is if you want this title, it'd be best to pick up a new MMr. You'll get your money back if it isn't your cup of tea, and for the most part they're problem-free. As far as the old vs. new argument-if you're not a restorer (I'm not) then go for a MMr. If you're a collector and history means something to you, the go for an original. Oh, and one other thing-these ARE NOT investments! Buy one, play it, have fun with it, keep it clean and maintained and if/when it comes time to sell, you'll get pretty much what you have into it back.