Bumpers are optional - skids and sliders are not. Have a look at your stock skid plates if you've got them - mine were scratched and DENTED pretty good after a trip up Rattle Snake Canyon. The dents on the gas tank skid were of great concern. Once your protected with them you can look at a front bumper for better approach angles and some extra protection. The rear bumper is totally optional.
Skids! If you drag your soft belly you can do alot of damage. Sliders will protect the hard to replace/fix sides. If you hit/drag your bumpers you will only damage something that you want to replace anyway.
sliders should be the first mod done to the x bar none. If I had to list mods in order of how I should have done them, it would be, mudflaps off, tubebars off, sliders on, rear swaybar off, upgrade rubber...
edit: after looking at your sig, I would go skids next!
I went the rear bumper route myself since the X doesn't have any stock rear recovery points (that I know of). Most of the trails around here are wet so there's a good chance of getting stuck in mud.. the rear shackles would come in handy if this were to happen (to me or if I needed to haul someone out). Sliders are next on my list though.