some already very good, bordering on great, players manage to step into the legendary league when given the added responsibility of captaincy.
imran khan is the prime example of this breed. allan border too comes into mind. some other good players like lloyd and steve waugh touched individual greatness when they were also asked to lead the team. even ranatunga played one level above his league as a skipper.
for some players captaincy somehow doesnt make much of a difference. viv richards and ricky ponting continued to bludgeon bowlers despite leading their teams through good and bad times for long periods. (i think ponting's recent slump in standards is age related. his coming back to form or fading away may have nothing to do with whether he continues as skipper or not). i would put gavaskar and greg chappell in this category as well.
for some players it is an obvious burden that it brings down their personal standards considerably. sachin tendulkar and ian botham were lesser players when they led their teams.
so..... yes. it does affect the individual's performance considerably. in team sports, captaining a cricket team must be the most challenging job.
the net worth of a player's career will be skewed by how long the captaincy stint lasted. ian botham's bad seasons as skipper dont sully his image as much as his fading years. but steve waugh's reputation is enhanced by his success as skipper. ponting, unfortunately, is going to be remembered less fondly than he deserves to be because of his teams losing in ashes and in india. that is because waugh and ponting led their teams for many years and are remembered as australian skippers while tendulkar and botham are merely great players who played under others most of the time, especially in the last few years of their careers.