burkjon: My question is, do you find these kinds of auxiliary features necessary to get the full immersive experience, or can you do without them?
I guess overall I'd have to say I can play games without these features. I've never really cared for haptic feedback in game controllers with the possible exception of the G27 racing wheel where it gives more of a feeling that you're driving a real car by providing resistance and can jerk the wheel out of your hands under certain conditions. I've always wanted to use EAX or surround sound for gaming but who realistically has 4-7 speakers set up around their chair in the correct orientation etc for gaming? I suspect 0.0001% of gamers ever use more than stereo with or without a sub and for anyone who might respond "That's not true because I do.", yes it is true and you're part of the 0.0001% (if not _the_ 0.0001% <grin>). :)
I had EAX set up once just to test it, but the front speakers were quite different from the rear speakers giving a different frequency response with the rear speakers having less bass and more treble which was highly noticeable and that ended up drawing me out of the game and giving me less immersion (in either Skyrim or TW3, I forget) so you need proper speakers for it to get the proper experience for sure.
I own a variety of specialty hardware such as Saitek flightstick, throttle and rudders, Logitech G27 racing wheel/shifter/pedals, and a NaturalPoint TrackIR 4 Pro head tracker. None of these devices are strictly necessary for any game, but each one of them can greatly enhance certain specific games or types of games to a degree that the difference they provide in the games is significant and increases both the realism and immersion and the enjoyment of gameplay. It's not subtle, but is rather highly noticeable and provides a completely different gaming experience that more than justifies the cost of the hardware for my usage case anyway.
The vibrating thing in my Logitech gamepads I disable however, don't care about that and find it annoying. Also kills the batteries.
What it really boils down to though is that these types of things are optional specialty features that some users may enjoy and find beneficial while others may not care for them, and still others are indifferent.