Is there any downside to using a larger than needed smoothing capacitor?
As far as caps go, there are two competing requirements:long-term (ripple) and instantaneous (spike).  A big electrolytic can give you the former but not the latter.  Generally you parallel your large electrolytic with a smaller 0.1uF capable of supplying that instantaneous spike whilst the electrolytic lumbers into action.  Or the 0.1uF may be for local decoupling to stabilise that regulator.  If the specified capacitor is actually 0.1uF or smaller, then the intention of the capacitor is to supply small amounts of charge very fast.  Do not replace this with a bigger electrolytic - that's definitely a case where larger is worse not better.

Going past that, you'll have to tell us what kind of regulators you're dealing with.  If it's just a basic linear regulator then it doesn't really matter.  If you have a switching regulator though, the capacitor will affect the resonant frequency of the switcher, so be very careful there.