I think no matter what Rig you decide to go with it will be worth it in the long run. Just get the best value for your investment and don't worry about ROI.
Nonsense, unless you want to randomly throw away money, ROI is very important. Difficulty will rise and it is not outside the realm of possibilities that some of these devices will not make you any profit. Problem is predicting future difficulty. If KNC ships in september, then that's 4-6 difficulty adjustments away from today. Difficulty could've doubled by then.
People always say it's not worth it, but you're investing on the possibility that maybe Bitcoin will go up in value.
If you are betting on the BTC price going up, you should just buy BTC and keep it in a wallet or a low-risk investment. It is a fallacy to reason that investing in something that incurs a BTC-loss is okay if the price of BTC goes up to compensate.
Plus, you can always sell your Rig later on.
For how much? The value of the mining rig will be inversely proportional to the difficulty. If the difficulty doubles, people will be willing to pay half of what they are willing to pay today. Unlike GPUs, which have a very popular alternative purpose (gaming) and retain a lot of resale value because of it, ASIC miners are solely for mining. If that isn't profitable, the miner won't be worth much.
I'm not saying that all ASICs are bad investments. Just be careful and run some numbers on pessimistic scenarios to see what your expected returns are. ASICs aren't get-rich-quick-machines.