Wow. Just wow.

Ok, for those who are clearly confused, imagine the following extreme scenarios:

A) You have 0% tooltip haste (which is actually 100% haste). DOT ticks once every 3 seconds for 3 damage. DOT lasts for infinite amount of time (read never needs to be refreshed). Your dps with this DOT is1 dps

B) You have 200% tooltip haste (read: 300%). DOT now ticks once every 1 second for 3 damage. DOT lasts for infinite amount of time. Your dps is now3 dps

C) Now, your dot has a finite length, say 10 seconds. It ticks every 3 seconds for 3 damage per tick. Your dps is 1.

D) Now, your dot lasts for 20 seconds. It ticks every 3 seconds for 3 damage per tick. Your dps is still 1.

The increase in dps from gaining more ticks, like going from scenario C to scenario D is NOT the extra tick itself. It makes no difference to the DOT dps. None. The extra overall dps you see comes from refreshing the DOT slightly less often. This means you save a GCD, which would then be used on a Mind Flay tick most likely. And no, you don't save a GCD with every refresh of the DOT. You save a little bit over time, infact i think it's after around 6 refreshes that you save a GCD which is roughly 100 seconds but somebody else can give the exact numbers. That's an extra Mind Flay tick every minute and 40 seconds, not huge.

DOTs will ALWAYS benefit from haste (as seen in Scenario A and B). Even beyond breakpoints. DOTs benefit from haste because they tick more often. Not for longer, but more often,notice that important distinction between more often and longer!i.e. the DOT frequency increases with haste.

The only exception to the above is DOTs that cannot be refreshed at will and hence will not have a 100% uptime, ever. Examples of these DOTs are Devouring Plague and Combustion. With these DOTs the opposite is true, extra ticks increase the overall damage of the dot that you would not otherwise have and increasing the frequency of these DOTs actually does not increase their damage. it only makes them slightly more "bursty" dps. For Spriests, the real increase in dps at the 8085 breakpoint actually comes slightly before when DP gains an extra tick. HOWEVER these DOTs are often very short tick duration (frequency) i.e. 1 second at 0% haste, so there are many breakpoints for these DOTs that don't require huge jumps in haste rating and the likely hood is that increasing your haste by any half decent amount will give you more ticks.

As for refreshing DOTs, the mechanics are the same as Cata in that buffs to you are applied at the time the DOT lands on the target and will not update dynamically. Debuffs on the target will update the DOT dynamically on a per tick basis.

Edited to say in my examples above I realise it's impossible for a DOT to tick every 3 seconds and last for 10 seconds, but you get the point