As ideas started to run dry, The Simpsons writers got lazy and decided to fill in the time wherever possible, something they've admitted themselves. It appears in the form of exceptionally long couch gags, and in irritating drawn-out "humour" which usually revolves around dragging out a simple, one-dimensional joke which might have been funny had it just been a moment long, for as long as possible. In this episode, we get three such moments:
1) Lisa running around the guinea pig rescue home's place shouting "OH MY GOD", "AWWW" and other such prattle for nearly two minutes. Two minutes of nothing, no plot progression, nada! For a show that's only 18ish minutes long, that's a considerable amount of fluff
2) Another half a minute of nothing but Homer going "woah woah woah".
3) Kirk going "errrrr" for a dragged out length of time in response to a question, and then the same scene recycled to the question followed.
None of these were funny, they were downright annoying and cringeworthy. When the series packed a massive punch in its heyday, it's literally painful to see the team trash it like this.
The final painful nail in the coffin is the 'moral' at the end; it doesn't matter whether something is a forgery or not, only whether it makes someone happy. That's neither a lesson nor a moral, that's morally bankrupt nonsense.
Without the original vision of a given artist, there would be nothing to copy, and therefore nothing to make people happy. So yes, forgery does matter. It's wrong, plain and simple.
A passable plot and passable humour that could have scored a 6/10 if it hadn't exemplified so exceptionally well the series' fall from grace.