Hi Michael,
O.K., if you run in professional mode, the cost aspect maybe different (I think it deeply depends on the individual tax situation).
Nevertheless saving money ist most often the better choice IMO :)
O.K. , do we need 24 GB or more Ram in five years ? Possible. But I would never buy a PC to be valid for a time scale that long. This doesn´t mean that I´d refuse and automatically throw it away, but actively planning with such an immense overhead, that a machine of today can compete with one in more than 5 years is possible but extremely expensive. Most often it is a better choice to just buy a new computer when the time comes.
Of course new installations are a very nasty point, expecially with hardware locked software products, all the serial numbers etc ( where was the plastic box with that tiny sticker forgotten about 6 years ago.......? ), but sometimes it is a good way to refresh the system setup anyway and migration tools also keep getting better.
I guarantee you that you will be sneeking around the $900 mid-sized-out-of-the-box gaming PCs, which every supermarket will sell in 4 years and offset the performance of the high end machines that we can buy now ( ....O.K we are not talking about IBM Blue Jean or something like that, not to speak of the often mentioned CRAY, "the only computer running an endless lopp in less than ..." :[:D] , at least you can sit on it and enjoy the waterfall cooling , by the way the German Tech Museum in Munich has one of that, everytime a must see/sit on....)
Coming to ECC , I didn´t follow the price lists lately, but I fear it will get expensive and you have not so many products to choose from. If you motherboard can handle it and you are willing to pay the price, go ahead, but I think this will bring you directly to the server platforms, because Intel usually shuts down the ECC support in their non server lines, although the controller could deliver it in theory. There may be workarounds (X58 series ? ) , but you have to make sure before buying.
I wouldn´t do it, if it would be for my system.
It maybe different for live TV broadcast applications or something like that, where I could understand it, but even if the sequencer crashes 1 in 10000 times because of a memory instability ...... in a studio environment Microsoft, Adobe, Flash, Shockwave, GFX , audiodrivers, and so on crashed 100 times before.
If you want to care for your RAM, cool it well. Put good ventilation into the PC casing and/or mount some extra heatspreaders if needed. Usually the modern RAM sticks come with them directly integrated, at least the better ones.
When you seek for performance -> Buy at least one SSD for the boot system. if you like it and there is some spare money also consider one for samples. Although I think we will see a big price drop for these items in the future, but as said in the beginning : Don´t look back on former price/performance rations when it comes to electronics.