Should I pay 500 to mod my old Mac MR-67 tuner?

I have owned a vintage Mac MR-67 for about a year. It's never been aligned or measured and I called Audio Classics about the process. They offer a full-Monty Richard Modafferi update/mod for $500, and I am about to go ahead and send my tuner in. My question, and only hesitation: should I only be spending this kind of money on a MR-71? Everyone seems to prefer the MR-71 but I've never heard one or compared it to my, or any, MR-67. I don't plan on trying to sell my MR-67 so I'm not really worried about covering my costs. I'm just wondering if I'd be spending too much money on the MR-67 when I should look around and get a MR-71 instead. My MR-67 is in great condition cosmetically, no rust or bubbles or anything.
Thanks for any thoughts from the tuner gurus.