@Angela G I don't think you need an in-house developer -- I'm technically a consultant and usually only spend a handful of hours on production Marketo integration code per month (but many more hours on experimental code I can use later if the need arises).
But you would benefit from having a skilled JavaScript/Marketo developer who you can call as needed, and that dev needs her/himself to be diving into Marketo on the regular -- you can be a rockstar JS developer in general, way better than me, and still have no idea what's going on with Forms 2.0 until you get past the learning curve. And no company wants to pay someone to learn from scratch, and then relearn if they haven't touched Marketo in months! (Unless, as you mention, they're on salary and it's understood.)
Re: sales, Marketo has vastly expanded their APIs of late. I imagine they're caught between [1] advertising developer extensibility as a major feature and [2] skipping over it as it may cause concern for some clients. Remember, if I hadn't chimed in to worry you, you'd still have @Josh's workaround! 🙂