To make a long story short: there's very little you can do. Currently, at least.
a) motion estimation & compensation/interpolation will *always* make errors
b) for compansation (target: denoising), the faithful scripter has *tons of possibilities* to check if a given compensation is "good" and can be used, or if it is bad and should not be used / replaced by a fallback solution.
c) for interpolation (target: rate changing), the faithful scripter can do *nothing*, because
c1) the plugins hardly offer any grips to hook in
c2) there's no reference frame one could compare the compensation with.
So, for the case of interpolation, you are fully at the mercy of the plugin coders. From the scripting side there is nothing that could be done, because the crucial points are out of reach.
Sidenote: if you need this stuff "at work", then IMHO the investment into a professional solution would be advisable, anyway.