From what I know, migrating the content is only possible to vBulletin 4.x (not 5.x) Even after this, migration will cause of a lot of issues with links to internal content (posts, images, etc.) in addition to the typical migration issues. There's usually a need to run scripts and manually tweak things to fix issues and an entire process which requires formal testing to make sure there is nothing screwed up. Don't want to deal with that.
CS is currently running on fairly premium infrastructure which is fast and responsive. The downside is that space and bandwidth is capped and we are reaching these limits, and the service isn't turnkey. I have to deal myself with occasional database cleanup and I don't have resources where I can submit tickets were I can get little things done.
It's possible to stay on this platform, but I would need SMF experts on retainer to maintain this site and also expand on its functionality. With the money raised, it would certainly be possible to do that. I hear people complain about the shitty SMF forum software and cosmetics, so I figured I'd move on to a full turnkey solution.