Everyday executives ask themselves the same question: do I buy, build or partner? Even if you have all the capital you need to acquire another company to fill a market need that your product doesn't have today, I recommend you look at partnering first to determine if the company you want to acquire his EAP good set culturally, technically and financially.
If you want to build it, like you say "going it alone", yes you will have more control but it will likely take you 2 to 3 times as long as you'd expect and even then your solution would probably pale in comparison to others that have been on the market enjoying the refinement from customer feedback and market feedback. All the while you're trying to build that new solution you'll also need to come up with messaging, marketing etc. and all the things you need for product to be successful - while working hard on that chances are the products are probably not getting the attention they used to get and therefore are not evolving and gaining market share like they should. Think about that cost when you think about building vs. partnering.