We've seen Kirk with his shirt off dozens of times, and he never has any body hair. Fair enough, it makes him seem sleek and well-groomed.
I think the notion that a shaved or waxed male chest constitutes part of being a well-groomed male is a fairly recent one stemming from the trend during the last 15 or so years of metrosexuality. If anything, Kirk might have seemed more manly during the 60s had he actually had a hairy chest.
As to why Nimoy didn't have his chest waxed, perhaps he didn't feel the need to apologize for looking like a man. In-universe, one might argue that Vulcans (like their Romulan cousins) are very virile and passionate; they just keep it under wraps. A hairy-chested Vulcan then would not seem out of place if one were to associate a male hairy chest with virility, potency, and strong masculine drives (i.e. as in Pon Faar).