Intuitive explanation for this hysteresis circuit?
What you have there is similar to an SCR but with the gate tied so as to turn it on. 

The hysteresis comes from the fact that BJTs (in this operating realm) have a lower Vce(sat) than Vbe- more like 0.2V than 0.5V When the voltage across the two transistors rises to Vbe * 2, you start to get significant collector current in the transistors, which is amplified by the transistors, leading to lower Vce in each, so you approach Vce(sat) * 2. 

The Vbe I mentioned of 0.5V is less than the typically quoted 0.6 or 0.7V because only a tiny bit of base current is enough to get the transistors going in the positive feedback loop. 

Keep in mind that the 'constant Vbe above which current flows' is kind of a convenient falsehood- some current will flow with any voltage across the junctions. In fact there would be no hysteresis (the thing would switch on immediately with any positive voltage) if the transistors had a constant \$\beta\$ with collector current , but they don't- the gain drops as the collector current drops, and at some point the loop gain is less than 1 and the circuit cannot latch on. So as the voltage rises you will see the (small) collector currents rise as well, tickling the dragon, until at some point (perhaps with a touch of noise) the loop gain exceeds 1.0 and the pair switches on. 

You might want to plot the base and collector currents in your simulation to see the relationships. You can also plot the betas and the product of the betas vs. voltage or current (or time) in PSPICE.