It depends on how much traffic your sites have but relatively slow sites can run on shared hosting without problems. I have a VPS with 1.5GB memory running Xenforo, 3 Wordpress sites and other static sites with tons of power to spare.
I have at least 6 wordpress blogs.
And I have 5 xenForo forums.
All powered by @Mike Edge's server.
At least 3 websites are grabbing the most amount of traffic, in general, they are all around 3 gigs, and the traffic is about 13 gigs a month. Peak months are worse. The highest I've seen it go is 22gigs.