no problem
I would imagine that as long as they are say... 25% stronger, it would be worth it. If you are seeing it green a lot of the time then I would say you are festering enough, or applying them at good times. Even with the normal Unholy playstyle I still tried to apply dots during trinket lined up procs, blood fury, ect. It was extra damage, so no reason not to. Now that I play fester-esk I apply less, but even before with normal I only applied maybe, once normal then once again before Outbreak came off CD due to a trink proc.
I generally reapply them whenever they are stronger as Unholy because I play a festerblight-esk playstyle (I try to keep em rolling long enough to reapp new stronger dots, but if they have to fall off for some reason I do not worry too much nor does it break my dps). It's always seemed to be pretty nice for me, and especially on fights like Jin'rok I will reapply them in the water and only in the water regardless of trinket procs outside, as the dots will never be stronger then
Blood Boil doesn't extend dots for blood, it reapplies them, so be careful with that. Once I got dkdots I noticed this because I would "refresh" them as I thought it was, and they would go down to a lower application of damage. Then one or two hits later, vengence made it stronger and was therefor a better dot to apply. So they replace, not refresh.