In
most cases, moving from a VPS to a dedicated server raises costs with minimal benefits. Trust me, I have had a dedicated server since '98.
You may see an increase in performance. That depends upon what hardware the two VPS boxes were built upon. If they were also 2 GHz Celerons with 1GB of RAM, you will see a performance improvement. But if they were Sun E10K's...
For me, what worked best was to create an almost meaningless holding company and then put all of my web projects under that company. Then, even if I sell off a project (web site, sub-company, whatever), my main operations do not need to be reorganized.