Prediction is useless, as even the quants with billion-dollar supercomputers can't do it. You can just try to put the odds in your favor. Better to stick to good stock picking than time markets.
For every argument, there is a counter-argument. For example:
The current P/E of the market hardly looks like the all-time bargain: S&P 500 P/E Ratio - Chart
(This is off Prof. Shiller's numbers, so you can put some confidence in them.)
And the three macro things that drive the market the most: 1) the direction of rates, 2) multiple expansion, and 3) the direction of inflation. Currently, rates are essentially zero (or negative if you look at "real" rates). So there is no room for them to go lower. Rising rates have historically coincided with a down market (because higher rates means your discounted future earnings are smaller).
Multiple expansion is a possibility, but with the chart, you can see it won't take much to go into overvalued territory.
That leaves inflation, which is not coming down like it did over the 20 year period of 80s-2000. It is most likely going to rise, again a negative development for the market.
Lastly, companies have blown out earnings because analysts sand-bagged their numbers and the companies have slashed costs/personnel to be conservative. Now that inventories have been refilled (the source of all the earnings for the past few quarters), there needs to be a pick-up in the demand side of the economy. Last I looked, people are still highly levered and no-one is giving out credit. Unless China or the developing world steps up, the demand side won't be there. And you get like Cisco -- who told analysts last week to crank down their projections...