Well for the dash and center console etc all the Vinyl work and stuff, i use ArmorAll Cleaning Wipes and Protectant (8 dollars each). When i first used it i saw a massive imporvement in the texture of the interior, it looks very nice, clean. Glass i use ArmorAll Glass wipes (8 dollars), but you really dont need to. (No i dont work for ArmorAll)
Depending on how good condition your paint work is, cut and polish usually makes it look brand spanking new. Im lazy and just use PolyGlaze (brand name) Cut and Polish (i think it was about 9 dollars), it comes premixed ready to apply. I used it on my car and it comes up great after a good cut and polish. Takes a little while but well worth it. Make sure you wash your car before it though.
Then you can always polish up the mags etc, get tyre shine the whole 9 yards.
Umm, for upholstery, im not to certain, ive never actually cleaned mine cause i have seat covers.
For sagging on your roof lining, you may have to replace it. Theres a great article on that here:
HOW TO replace headlining - Very detailed
If all else fails, go down to SuperCheap auto, and browswe the cleaning isle. And just read the backs of stuff see what they offer.
Hope thats been of some help mate.