personally, i don't think they can reverse or stop any damage (sun, smoking), but think they're a good preventative measure. i've been moisturizing regularly for 10.5 years & am thankful that i don't have any visible/noticable wrinkles.
i great skin is dependent on genetics & lifestyle (diet & exercise). someone like Jan Michael Vincent aged 20 years in something like <10 years b/c of his hard partying lifestyle. if you eat & drink hard, it'll show in your skin. if you eat healthy, it shows in your skin.
i've seen before & after pics of people who've done chemical peels, professional Microdermabrasion & am amazed. however, years of sun damage & hard living can't be erased overnight or in 1-2 visits to the doctor.
i don't know much about AHA/BHAs, but know that some people benefit from it. all i can say is use what works for you, eat healthy, drink in moderation & stay out of the sun or use a sunblock.