As I understand it, VSTA is not a 'new VBA' nor built into Office 2007, but a separate 'Super-VBA with .NET' that must be licensed from Summit, and distributed as part of an external application. I think it's just targeted at ISVs wishing to extend Office, but the blurb about it also contains this gem:
Perhaps the feature most applauded by enterprise BDMs and SI’s is that VSTA customizations are seamlessly opened by any version of Visual Studio enabling professional developers to continue to enhance applications originally created by end user developers – a feature requested by many enterprises because applications often grow in sophistication over time.
I've not bothered googling BDMs and SI means le Système International d'Unités to me, but I took this mean that you can take the horrible mess of excel VBA that your traders used to turn worthless morgages into goldmine CDOs (and then bailouts), and your 'real developers' can open it in Visual Studio and sort the mess out (or just quit...).
also VBA and VSTA can exist together:
http://blogs.msdn.com/vsta/archive/2006/07/31/684514.aspx