Truth is, I don't spend too much time thinking about such issues.
That's because 1) I don't have any special insights regarding such matters; 2) Hardly anyone can get it right; and 3) Getting a macro call right need not mean you can invest correctly.
So I just focus on evaluating businesses, and making sure I stick to simple ones I can understand. A lot of value investors got killed with opaque banks during the last big financial crises because it was too hard to understand what the banks are doing. Conversely, it's a lot easier to see what can trouble say, a Starbucks (weak consumer spending, high coffee prices).
One barometer I like to use as a pulse for the US's economic health is Berkshire Hathaway. Buffett's company owns the second largest railroad and one of the US's largest utilities. In Q2 2015, Berkshire's non-insurance businesses (the rail roads, utilities, and other industrial companies), saw operating earnings grow 8% year-on-year. That's not too bad.
There are always things to worry about. But it's good to classify them as things u can know and control, and things u can't know and can't control. A lot of macro worries belong to the latter; let them be.
As for slow growth. It's good to look back to 1992. The US had an awesome time in the 1990s leading up to the dotcom bubble. But not many realise 1992 was horrible. There was a recession, unemployment was high, growth was slow, and even Ray Dalio was bearish on stocks.
But then the internet came and changed things dramatically. Have some faith in human ingenuity. Betting on the stock market is a long-term bet that we humans are always striving to improve our lives in aggregate :)