There are 500k+ apps on the app markets and competition is fierce. It is paramount to have great UX and graphics.
Cross-platform tools are NOT on par with native development. If they were, we would all be using them. But we are not. With a reason – you do NOT have full control. And full-control is necessary to have great looking apps.
If your app is not a consumer app, but an enterprise app, which use is dictated by some internal department, then you might get by with so-so design, because the value of such app is in it’s functionality.
But, if you are serious about mobile apps market – then the only way is to go native. And you need an UX guy and a designer (who knows mobile development) on team full time. You will spend upwards of 50% of time on looks. The project that I’m part of now is spending 80%+ of time on looks (graphics, animations, UX, usability testing).
A suggestion: spend a reasonable amount of time (= days) using you competitors apps. Also spend time with top 50 apps on each market. You will get a feeling how high the bar is. Then check apps made with cross-platform tools (you can find links on their sites) and compare.