I don't think you will outgrow RealStudio anytime soon since you can do a lot with it straight out-of-the-box. Besides just because you get a new development tool doesn't mean you have to give up on VB, use the right tool for the job. Even though the framework is different between VB and RealBasic it's still the Basic language so all the basic syntax would be the same. All iterations, such as loops, work exactly the same. Selections such as If statements and Select Case blocks works the same way. The value types are the same. The object oriented notation are the same. The various objects will of course differ but even if you just stay with one single language you will always encounter new APIs which you need to learn anyway.

So I did not mean that you shouldn't try out RealBasic, you just asked for the differences and I pointed out some of them and also tried to explain what you can expect from the different editions of RealStudio and which one you should get if you want to develop for more than one platform. So I would still encourage you to download the trial version of RealStudio and try it out, the true advantage is of course that you can develop for both OS-X and Windows. In all honesty to be able to develop for Mac without using C/C++ or the terrible mish-mash language that is Objective-C could very well be worth $299.