I wanted to get back to you on this. Honestly, I think it would be a waste of $30, but it's up to you.
Your $30 gets you 3 months worth of upgrades only. Our "official" version is 3.84, but I actually manually fixed the problem that was fixed with 3.85, so we're really running 3.85. 3.86 is the most recent version out - but its original release made such a huge security hole in the software that the news story was picked up by the BBC. I've heard that 3.87 will be the final 3.8x version released, and so the last that we would have access to. I can't guarantee that it would be released in the next 3 months though.
Basically, I don't really have confidence that any future upgrades are going to be written correctly. But there is always a security risk not having the latest version. It's hard to say how much and my personal feeling is not much, but it is a risk. I sort of feel like if a hacker wants to take down your site, they'll find a way though.
Long story short, it's up to you. I don't think I'll be taking advantage of it for myself though.