There is no doubt that a dedicated virtual RAM is very important for a VPS. Most people try to purchase more virtual RAM than they need. But in my opinion, you don't need to purchase too much RAM. In term of VPS, it is very flexible, most VPS provider support to upgrade your VPS anytime.

If you need a VPS for blog, I'm sure that 2GB RAM is completely enough for the beginning. And I'll recommand you some 2GB VPS providers.