While I agree it's not the right time to build a new rig, the drop off of mining earnings from today shouldn't be 40%.

If I'm wrong here, please let me know, but the block rewards would be a base minimum of 2 ETH (like today) plus any tips.  So even if there are no tips, a block reward will still be 2 ETH.

For ethermine, the most recent block rewards are in the 2.1 to 2.4 range.  That would be about a 4% to 15% drop to 2 ETH.  Even the higher rewards of 2.6 would only be a ~23% drop.  You have to get into block rewards of 3.3+ Eth to see a 40% reduction.

So it will have an effect, but it's not going to be nearly as bad as some people think.  Plus there's the probability that the value of Eth rises.

With all that said, right now, $2k USD would be better spent on Eth directly instead of a GPU to mine it.