popo, cosmetic dentistry isn't a recognized specialty...any dentist who graduates can hang out a shingle and call themselves a cosmetic dentist...all general dentists learn how to perform cosmetic procedures...as for endo, it usually requires a year of GPR (slave labor) after dental school before you can get in (i believe that's because it's a very tactile specialty...you MUST be great with your hands, from what i've heard)...it's hard to get into, unfortunately, but i don't think it's quite as hard as ortho or surg (probably have to be top third of your class, as opposed to top ten, but don't quote me on that)...maybe that's because endo is considered very boring and repetitive...i observed an endo briefly, and he didn't seem too satisfied with his job, but occasionally he makes $5000 a day...decide what makes you happy...good luck...
p.s. you can make a fortune at perio and pedo as well...and perio is considered relatively easy to get into (i think it's the most popular specialty after ortho and surg)...people tend to avoid it because it's very bloody, and perio surgery is physically taxing to perform...pedo's deal with all the challenging cases the GP's don't want to treat, and kids often go nuts in a dental chair (i don't think i'd have the patience for it)...but again, big $$$ are to be found in any specialty...don't worry so much: even if you don't specialize, you can take your DDS or DMD and move to an underserviced area and be the only dentist for miles around -- i know of one guy who did this, and patients were lining up outside his office when he opened his practice...i was told he TAKES HOME about $300,000...don't ask me how, i think he must make that money on hygiene...the opportunities are there, my friend...