I've been in the same situation as you. Got asked to leave by my hosting company 3 times already and each time, our forums would be down for 72~ ish hours.
We started on a shared hosting environment, moved to VPS and then lately to dedicated.
Although my knowledge about dedicated servers is pretty limited, I've decided to go ahead with it and learn a bit. I've also paid a server management company for 1 month to help me get it up. Took me about 3 days to optimise and such.
However, I've recently stumbled across this:
http://www.globalgold.co.uk/dedicate...m_hosting.html . They're pretty knowledgeable about vBulletin and even if you use too much CPU resources, they'll talk to you before kicking you out. I've had a couple of talks with one of their sales representative and it was really tempting to cancel my dedicated and go with them.
Good luck!