I have the MODAFFERI mod MR-77which went for about $ 500 more. I have had several top tuners including an MR-71 modded by another tech. IMHO the tubes just sound better, period. As to which model is "best", opinions differ wildly with individual application. I don't like the way the MR-78 looks, so I am cheered when others say it was sound compromised to get better sensitivity- but I suspect all of these "fan club" reports are mere bias.
As for tube life, by the time you need new tubes, you will also need a new alignment, so just relax ad enjoy.
As for tube life, by the time you need new tubes, you will also need a new alignment, so just relax ad enjoy.