You don't need to invest in all that kit if you don't want too - I have most of the pretty typical "kit" for a flight simmer, yet I'm often too lazy to haul it all out and set it up (I don't leave it out in between "sessions" since I work from that computer too).

So, very often I wind up flying with just my cheap Logitech joystick, but even an XBox controller would be a huge step up from mouse/keyboard only.

Having programmable buttons available at your fingertips without having to take your eyes off screen and look for a button really adds to the immersion in my opinion.