It depends, as usual.
What genre? How much money/time do you have? Do you develop the application to make money?
Users are generally surprisingly forgiving about bad input controls in niche games (e.g. JRPGs by independent developers), but better input control is still a plus if you want to sell more.
If you are on a very tight budget and do not directly profit from sales (e.g. a charity fund paying you a fixed amount of hours to develop education software), it's sensible to stick to one single input method done well - doing multiple input methods well takes considerable amounts of time.
If you want to sell your game at a reasonable price ($20+) and aim to reach a reasonably large number of buyers (50'000+), you absolutely should keep in mind* the different requirements of mouse, keyboard, touchscreen, and gamepad devices from the beginning. There's no way to simply "retrofit" gamepad input on a mouse/keyboard game or vice versa.
*When thinking of how to make your game touch, gamepad and mouse friendly, you may find that there doesn't actually exist a good solution. Such cases are quite common (real time strategy games are rarely cross platform). In those cases the usual solution is to only release on devices that support the form of input your game requires.