I have two thoughts on this. I've had a coupele of Audio Research components in the past. Seems like everytime I turned around, there was another MK something for my amp or preamp that was just an amazing breakthrough for two grand and up. That got fairly frustrating. About 8 months after I bought my Meitner rig, here comes the SE upgrade for 5 grand. Now that DCC-2 cost about 12 grand new. So with no dealer markup, no shipping, no marketing, when the probable actual cost of manufacture was about 3 grand originally,they now want 5 grand for an "amazing" upgrade. I have elected not to participate. All of the above has been tres frustrating. However, when I got the upgrades on the Audio Research Ref2, the sound was unmistakably better but I am not sure the VT100 upgrade to me made that much of a difference. So maybe the Meitner upgrade is "amazing". I don;t want to spend 5 grand without hearing it. Hell if they are so sure it is amazing, let me borrow one for a week and compare it to my non-SE version. And then about every five years or so it seems that even the upgrade guys come up with new lines anyways. Probably some engineers are driven to continually do better, which ones they are I won't know until I listen to it. But it is always my option to upgrade or not, and there are no aestetic changes for my wife to complain about. Upgrades are also cheaper then replacements if I get "upgradeitis, it still leaves money to save for my kids college fund:)
Now let;s take the other mfrs. like Krell. About every two years they come up with a new line, the WAF factor goes to hell because if you keep your old Krell, it no longer matches. It is a new box at new prices. Once anybody replaces a line, in any industry, the old line plummets. Look at the huge discounts on the old body styles of Merceces S and CL series right now. But with Krell, you get a brand new look, and hopefully, more than just a few mods to the box. One thing though, it is much easier to compare your old box at home to the new box borrowed from the dealer. Much harder to get the dealer to let you compare MK1 to MK3 at your home. So in my opinion you can make a much more informed opinion on a new box before you buy, and, afterall, nobody is twisting your arm.
In this day and age, everything in electronic advances are accelerated. The days of buying a Hewlett Packard 8566b spec an and having it be the best 22ghz spec an for 20 years are gone. Which is why, finding a dealer you can trust is absolutely worth the money. A good dealer will tell you in their opinion whether an upgrade or replacement is worth it or not. They listen to this stuff day in and day out, they talk to the mfr., they can compare it on a variety of gear. They can help stop the big mistakes one can make. One of the things I like to do when I get the upgrade bug is check the stereophile listing with components that have been recommended for three years or more, to me it means that the mfr is satsified enough with the product and thought process, and put enough thought in ahead of time, that it doesn't need replacement, modification or upgrade in six months after it is introduced. It also probably is axiomatic that it sells well enough and reviewed well enough that the mfr feels no compelling need to make changes to the unit. Good reason to audition that unit I think.
