It really depends. Sure the damage was more consistent before, but a few crits could easily make our DPS shoot up. The problem is, what will the bonus be? Shadow Power only affects Flay, Blast & sw:d, so if we're getting anemic crits for our dots after getting a high mana/dps ratio with the straight +% damage, we're going to have some trouble.

Let's say VT gets +100% damage on a crit. if you have ~20% crit and were ticking VTs around 1.3k, now they'll tick for 1040. Let's say then that 1 VT cast would reliably give you 1.3k DPS, and now it always gives you at least 1k DPS. Let's say VT ticks 15 times. If you have a ~20% crit chance, you'd expect about 3 crits per VT. So that brings your expected DPS to:
(1040*12 + 2080*3) / 15 => 1248, which is an overall difference of ~4%, on the average. So where do things even out? Sure, it depends a lot on spellpower and talent buffs... but even calculating it straight.

Let's say we'll get +100% damage on dot crits:

850*15 = 12750 'standard' VT, no spellpower

((12750* (1+crit))+ spellpower) / 15 => old VTDPS
( ((850*(15-(1/crit))+spellpower)+((850*(1/crit)+spellpower)*2) )/15 => new VTDPS

so... when these are equal, VTDPS is equivalent.

isolating some terms:

(multiply all by 15)

(12750*(1+crit))+spellpower - (850*(15-(1/crit)))+spellpower + 850*(1/crit)+spellpower)*2 =>

(div by 2, subtract spellpower from spellpower)

(6375*(1+crit)) - ( (425*(15-(1/crit)))+(850*(1/crit)+spellpower)) =>

(div by 425, simplify 2*(1/crit))

(15*(1+crit)) - ( (15-(1/crit))+( (2/crit)+spellpower) )

So, presuming 100% crits, this is the differential in VTDPS.

Let's see what the effect on spellpower is...

15*(1+crit) = 15-(1/crit) + ((2/crit)+spellpower) =>
15*(1+crit) - 15+(1/crit) - 2/crit = spellpower =>
1+crit - 1+(1/crit) - 2/15*crit = spellpower/15 =>
15/15*crit + 15/(15*crit) - 2/15*crit = spellpower/15 =>
(13/15) * crit + 15/(15*crit) = spellpower/15 =>
13*crit + (225/(15*crit)) = spellpower

So... let's say you have ~20% crit:

(13*crit) + (225/(15*.2)) => 77.6 spellpower

So, the difference between old VT & new VT will be equivalent to about a 77.6 spellpower change if you have ~20% crit and we get a +100% damage on VT crits. Some of my algebra may be a bit off (it's pretty late for me), but it seems that we'll lose about 77.6 spellpower with this change... except... we're getting Divine Spirit baseline. I'm not sure if the Imp Divine Spirit talent is going to stay, but if we can pick it up, it will cover that lost spellpower.

This is all presuming 100% crits, if the crit coefficient is smaller for DoTs, we'll likely lose more effective spellpower on VT, but we may gain on other DoTs that have coefficients. I'll leave it to more awake people with better info to figure all that out.

What is the ponit? I should go to sleep. What is the other point? There well be an effective spellpower change, and it may push our DPS up overall. Without any numbers to back it up though, I think we'll lose about 4% to 5% DPS off the top unless we can pick up Imp Divine Spirit somehow.