For people playing at home, cheap boards and USB3 are the two reasons for going to 2011-3. If you have a board and can get away with less USB or an add in, v3/v4 dont make sense yet. Wait a couple years.don't know if i completely bought into the ddr4.... sure, if you ever come to max out the memory and if you do then you have the money and wouldn't really be asking much about cost
but for the majority of us who never come close to the need or have enough money to be able to max out ddr3 that you would actually need to have a ddr4 board to be able to hold more ram, ddr4 just just a huge cost step up for minimal benefits and bandwidth over ddr3....
If buying for a client, I am going to get something new not 4yo stuff off ebay.
I personally got a 2696v2 coming, I own a board and ram already. For what I am doing, throwing more cores at it works well.