Well - I measure the valkue of "Add-Ons" in two categories. 1) How enjoyable is my ride and how well can I recover from the un-expected trail hazard, and 2) how far am I willing to walk should I have a problem.what is with people and "needing" huge tanks and custom suspension?? deal with the regular suspension and carry a small canteen with a quart of gas in it! or just fill some powerade bottles with gas, cuz gas doesn't melt those bottles. Why would you spend 200+ dollars on something that isnt necessary? i say case saver skid plate and bark busters and you are good to go! of course... basic tools too
On Item #1: I can personaly say that suspension that has been properly set-up for a particular rider (Doesn't necessarily mean fully custom suspension but maybe some vavle and spring work) pays for itself everytime. Not having the fight the bike and being able to take the big hits, ruts, etc that are sometimes unavoidable makes the ride so much more enoyable.
On #2: I often ride far from roads / camp and I don't like to walk. So I run a larger tank and carry with my just about all the tools / parts I would need to get me back home, even limping back home. All it takes is one 10 mile hike in motocross boots to have you re-think your strategy. My "Supplies" have helped other riders more than me, but I figure that's just good Karma!!