That's why it's so detrimental to see a DPS spam dispel without much consequence. Blizz had stated that they don't want PvP to be whoever can press their dispel the fastest. It's hard to balance dispels from a DPS's point of view because mana is practically a non-issue for them. The anti-dispel talents were taken out, and a 5 minute CD can be countered by spamming dispel for 5 seconds.
Increasing mana costs for dispels, I think, won't change much. That's why I propose adding a 3-5 second CD onto all offensive dispels.
This wouldn't solve everything, and I don't believe it should. Buffs should have counters. Guardian Angel and Lifebloom should have weaknesses. It's the overabundance that's excessive.
Give all offensive dispels a short (3 - 5 sec) CD.